subject:"\[deal.II\] Q\: Question about extracting part of a vector"

Re: [deal.II] Q: Question about extracting part of a vector

2023-08-03 Thread Wolfgang Bangerth


On 8/3/23 05:01, Najwa Alshehri wrote:
The first scenario involves directly using the FeFieldFunction when my 
computed solution consists of a single component. In this case, I have 
successfully calculated the L2 and H1 norms of the error using the 
`integrate_difference` and `compute_global_error` functions. The calculations 
proceeded smoothly, and the execution speed was reasonable.


However, the second scenario involves using the FeFieldFunction when the 
computed solution consists of two components. My objective is to calculate the 
error for the first component only. To accomplish this, I employed the new 
VectorFunctionFromScalarFunctionObject class locally. Unfortunately, the 
computation of the L2 norm in this case was considerably slow and the H1 norm 
was very slow.


Given the current situation, I have two questions that I hope you can assist 
me with, as you have done in the past:


1. Regarding my specific project, is there an alternative method, other than 
the FeFieldFunction, to save the deserialized solution as a function and 
utilize it as the exact solution? It is crucial that the solution be saved in 
the first component of a vector with two components.


2. In a more general sense, how can I test this function to determine if the 
sluggishness is solely attributable to the FeFieldFunction? Additionally, I 
would like to verify whether the function is functioning correctly or not, to 
be able to send it in a pull request to the dealii git repository.


Najwa:
I don't know why the run time should be substantially slower for a system of 
two components than for a single scalar problem. That might be worth 
investigating. If you wanted to look into this, it would be useful to start 
with as small a program that shows the issue.


In general, FEFieldFunction is slow because it doesn't know where the function 
should be evaluated. If you give it a point, it first has to find the cell the 
point is in, and then compute the reference coordinates of that point, etc. 
You probably do this many times if you want to evaluate the solution on the 
quadrature points of a whole triangulation. This will never be fast


There are perhaps better ways to deal with the situation. For example, instead 
of doing the integration on the coarse mesh, you could take the coarse 
solution, interpolate it onto the fine mesh, and then do the integration over 
the fine mesh -- because there you can then just compute the values of both 
the coarse and fine solution at the quadrature points of the fine mesh using 
FEValues. This is fast, and the interpolation to the fine mesh should also be 
reasonably fast.


There are also faster but more specialized alternatives to FEFieldFunction. 
FEPointEvaluation is one option, though I don't know that class well enough.


Best
 W.

--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/


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Re: [deal.II] Q: Question about extracting part of a vector

2023-08-03 Thread Najwa Alshehri

Dear team,

I want to express my gratitude for the support you have provided thus far. 
I would like to provide you with an update on the current situation and 
seek your assistance regarding a couple of issues.

Firstly, I have successfully implemented the missing function 
`VectorFunctionFromScalarFunctionObject::gradient()` in my project. 
Although it appears to be functioning correctly, the execution speed is 
extremely slow. In fact, it took until the next working day to obtain the 
results for only two cycles of refinement. Based on the response from 
@Wolfgang, it seems that the issue lies with the FeFieldFunction.

Allow me to provide some context. I have a reference solution serialized on 
a fine mesh. In my current code, my objective is to deserialize this 
solution and utilize it as the exact solution. To achieve this, I have 
employed the FeFieldFunction. Now, I have two scenarios in which I need to 
utilize the FeFieldFunction.

The first scenario involves directly using the FeFieldFunction when my 
computed solution consists of a single component. In this case, I have 
successfully calculated the L2 and H1 norms of the error using the 
`integrate_difference` and `compute_global_error` functions. The 
calculations proceeded smoothly, and the execution speed was reasonable.

However, the second scenario involves using the FeFieldFunction when the 
computed solution consists of two components. My objective is to calculate 
the error for the first component only. To accomplish this, I employed the 
new VectorFunctionFromScalarFunctionObject class locally. Unfortunately, 
the computation of the L2 norm in this case was considerably slow and the 
H1 norm was very slow.

Given the current situation, I have two questions that I hope you can 
assist me with, as you have done in the past:

1. Regarding my specific project, is there an alternative method, other 
than the FeFieldFunction, to save the deserialized solution as a function 
and utilize it as the exact solution? It is crucial that the solution be 
saved in the first component of a vector with two components.

2. In a more general sense, how can I test this function to determine if 
the sluggishness is solely attributable to the FeFieldFunction? 
Additionally, I would like to verify whether the function is functioning 
correctly or not, to be able to send it in a pull request to the dealii git 
repository.

Your guidance and expertise in resolving these issues would be greatly 
appreciated.

Thank you once again for your continued support.

Best regards,

Najwa

On Tuesday, August 1, 2023 at 12:50:27 PM UTC+3 abbas.b...@gmail.com wrote:

> Najwa, 
> The files I edited are in the pull request here: 
> https://github.com/dealii/dealii/pull/15805.
> Let me know if I can help in a better way or of there is something I can 
> do. 
>
> Abbas. 
>
> On Tuesday, August 1, 2023 at 5:48:41 AM UTC+2 najwaa...@gmail.com wrote:
>
>> Hello Abbas,
>>
>> Thank you for your response. I have actually written something, but I 
>> need to test it. It would be great to have a look at your work as well, so 
>> we can compare.
>>
>> Best regards,
>> Najwa
>>
>> On Mon, 31 Jul 2023 at 10:48 PM Abbas Ballout  
>> wrote:
>>
>>> Najwaa, 
>>>
>>> I submitted a pull request  
>>> recently about something similar 
>>> . (I guess)
>>> Maybe that would help. 
>>>
>>> Abbas 
>>>  
>>>
>>> On Monday, July 31, 2023 at 7:37:59 PM UTC+2 najwaa...@gmail.com wrote:
>>>
 Dear Wolfgang,

 Thank you for your answer. I will try to write a patch to the deal.II 
 sources that implement the missing function. This might require some time. 
 I will come back here if needed.

 Thank you all for your quick answers,
 Najwa

 On Wednesday, July 26, 2023 at 11:41:15 PM UTC+3 Wolfgang Bangerth 
 wrote:

> On 7/26/23 12:17, Najwa Alshehri wrote: 
> > 
> > Regarding the function "VectorFucntionFromScalarFunctionObject," I 
> have 
> > observed that it works for computing the L2 norm of the error. 
> However, when I 
> > attempted to compute the H1_seminorm of the error, I noticed that 
> the gradient 
> > was not implemented for this function. Please let me know if my 
> understanding 
> > is incorrect, as I referred to the  for 
> this. 
>
> Yes, correct. Someone needs to implement 
> VectorFucntionFromScalarFunctionObject::gradient() 
> and/or 
> VectorFucntionFromScalarFunctionObject::gradient_list() 
> in exactly the same way as the value() and value_list() functions are 
> implemented. 
>
>
> > Could you kindly advise me on the simplest way to accomplish this? 
>
> The easiest way is to create a class derived from 
> VectorFucntionFromScalarFunctionObject in your own project that 
> implements the 
> missing

Re: [deal.II] Q: Question about extracting part of a vector

2023-08-01 Thread Abbas Ballout

Najwa, 
The files I edited are in the pull request here: 
https://github.com/dealii/dealii/pull/15805.
Let me know if I can help in a better way or of there is something I can 
do. 

Abbas. 

On Tuesday, August 1, 2023 at 5:48:41 AM UTC+2 najwaa...@gmail.com wrote:

> Hello Abbas,
>
> Thank you for your response. I have actually written something, but I need 
> to test it. It would be great to have a look at your work as well, so we 
> can compare.
>
> Best regards,
> Najwa
>
> On Mon, 31 Jul 2023 at 10:48 PM Abbas Ballout  
> wrote:
>
>> Najwaa, 
>>
>> I submitted a pull request  
>> recently about something similar 
>> . (I guess)
>> Maybe that would help. 
>>
>> Abbas 
>>  
>>
>> On Monday, July 31, 2023 at 7:37:59 PM UTC+2 najwaa...@gmail.com wrote:
>>
>>> Dear Wolfgang,
>>>
>>> Thank you for your answer. I will try to write a patch to the deal.II 
>>> sources that implement the missing function. This might require some time. 
>>> I will come back here if needed.
>>>
>>>
>>> Thank you all for your quick answers,
>>> Najwa
>>>
>>> On Wednesday, July 26, 2023 at 11:41:15 PM UTC+3 Wolfgang Bangerth wrote:
>>>
 On 7/26/23 12:17, Najwa Alshehri wrote: 
 > 
 > Regarding the function "VectorFucntionFromScalarFunctionObject," I 
 have 
 > observed that it works for computing the L2 norm of the error. 
 However, when I 
 > attempted to compute the H1_seminorm of the error, I noticed that the 
 gradient 
 > was not implemented for this function. Please let me know if my 
 understanding 
 > is incorrect, as I referred to the  for 
 this. 

 Yes, correct. Someone needs to implement 
 VectorFucntionFromScalarFunctionObject::gradient() 
 and/or 
 VectorFucntionFromScalarFunctionObject::gradient_list() 
 in exactly the same way as the value() and value_list() functions are 
 implemented. 


 > Could you kindly advise me on the simplest way to accomplish this? 

 The easiest way is to create a class derived from 
 VectorFucntionFromScalarFunctionObject in your own project that 
 implements the 
 missing function. The better way is to write a patch to the deal.II 
 sources 
 that implements the missing function because then others can use your 
 work in 
 the future as well :-) 


 > On a side note, although "VectorFucntionFromScalarFunctionObject" 
 works with 
 > the L2 norm of the error, it is quite computationally intensive. 

 It isn't VectorFucntionFromScalarFunctionObject that's expensive, but 
 the 
 FEFieldFunction. That's sort of inherently the case with this class. If 
 you 
 can, it should be avoided and you should try an evaluate the FE field 
 you have 
 at regular quadrature points, via FEValues. 

 Best 
 W. 

 -- 
  

 Wolfgang Bangerth email: bang...@colostate.edu 
 www: http://www.math.colostate.edu/~bangerth/ 


 -- 
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>>  
>> 
>> .
>>
>

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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-31 Thread Najwa Alshehri

Hello Abbas,

Thank you for your response. I have actually written something, but I need
to test it. It would be great to have a look at your work as well, so we
can compare.

Best regards,
Najwa

On Mon, 31 Jul 2023 at 10:48 PM Abbas Ballout 
wrote:

> Najwaa,
>
> I submitted a pull request 
> recently about something similar
> . (I guess)
> Maybe that would help.
>
> Abbas
>
>
> On Monday, July 31, 2023 at 7:37:59 PM UTC+2 najwaa...@gmail.com wrote:
>
>> Dear Wolfgang,
>>
>> Thank you for your answer. I will try to write a patch to the deal.II
>> sources that implement the missing function. This might require some time.
>> I will come back here if needed.
>>
>>
>> Thank you all for your quick answers,
>> Najwa
>>
>> On Wednesday, July 26, 2023 at 11:41:15 PM UTC+3 Wolfgang Bangerth wrote:
>>
>>> On 7/26/23 12:17, Najwa Alshehri wrote:
>>> >
>>> > Regarding the function "VectorFucntionFromScalarFunctionObject," I
>>> have
>>> > observed that it works for computing the L2 norm of the error.
>>> However, when I
>>> > attempted to compute the H1_seminorm of the error, I noticed that the
>>> gradient
>>> > was not implemented for this function. Please let me know if my
>>> understanding
>>> > is incorrect, as I referred to the  for this.
>>>
>>> Yes, correct. Someone needs to implement
>>> VectorFucntionFromScalarFunctionObject::gradient()
>>> and/or
>>> VectorFucntionFromScalarFunctionObject::gradient_list()
>>> in exactly the same way as the value() and value_list() functions are
>>> implemented.
>>>
>>>
>>> > Could you kindly advise me on the simplest way to accomplish this?
>>>
>>> The easiest way is to create a class derived from
>>> VectorFucntionFromScalarFunctionObject in your own project that
>>> implements the
>>> missing function. The better way is to write a patch to the deal.II
>>> sources
>>> that implements the missing function because then others can use your
>>> work in
>>> the future as well :-)
>>>
>>>
>>> > On a side note, although "VectorFucntionFromScalarFunctionObject"
>>> works with
>>> > the L2 norm of the error, it is quite computationally intensive.
>>>
>>> It isn't VectorFucntionFromScalarFunctionObject that's expensive, but
>>> the
>>> FEFieldFunction. That's sort of inherently the case with this class. If
>>> you
>>> can, it should be avoided and you should try an evaluate the FE field
>>> you have
>>> at regular quadrature points, via FEValues.
>>>
>>> Best
>>> W.
>>>
>>> --
>>> 
>>> Wolfgang Bangerth email: bang...@colostate.edu
>>> www: http://www.math.colostate.edu/~bangerth/
>>>
>>>
>>> --
> The deal.II project is located at http://www.dealii.org/
> For mailing list/forum options, see
> https://groups.google.com/d/forum/dealii?hl=en
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> .
>

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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-31 Thread Abbas Ballout

Najwaa, 

I submitted a pull request  
recently about something similar 
. (I guess)
Maybe that would help. 

Abbas 
 

On Monday, July 31, 2023 at 7:37:59 PM UTC+2 najwaa...@gmail.com wrote:

> Dear Wolfgang,
>
> Thank you for your answer. I will try to write a patch to the deal.II 
> sources that implement the missing function. This might require some time. 
> I will come back here if needed.
>
>
> Thank you all for your quick answers,
> Najwa
>
> On Wednesday, July 26, 2023 at 11:41:15 PM UTC+3 Wolfgang Bangerth wrote:
>
>> On 7/26/23 12:17, Najwa Alshehri wrote: 
>> > 
>> > Regarding the function "VectorFucntionFromScalarFunctionObject," I have 
>> > observed that it works for computing the L2 norm of the error. However, 
>> when I 
>> > attempted to compute the H1_seminorm of the error, I noticed that the 
>> gradient 
>> > was not implemented for this function. Please let me know if my 
>> understanding 
>> > is incorrect, as I referred to the  for this. 
>>
>> Yes, correct. Someone needs to implement 
>> VectorFucntionFromScalarFunctionObject::gradient() 
>> and/or 
>> VectorFucntionFromScalarFunctionObject::gradient_list() 
>> in exactly the same way as the value() and value_list() functions are 
>> implemented. 
>>
>>
>> > Could you kindly advise me on the simplest way to accomplish this? 
>>
>> The easiest way is to create a class derived from 
>> VectorFucntionFromScalarFunctionObject in your own project that 
>> implements the 
>> missing function. The better way is to write a patch to the deal.II 
>> sources 
>> that implements the missing function because then others can use your 
>> work in 
>> the future as well :-) 
>>
>>
>> > On a side note, although "VectorFucntionFromScalarFunctionObject" works 
>> with 
>> > the L2 norm of the error, it is quite computationally intensive. 
>>
>> It isn't VectorFucntionFromScalarFunctionObject that's expensive, but the 
>> FEFieldFunction. That's sort of inherently the case with this class. If 
>> you 
>> can, it should be avoided and you should try an evaluate the FE field you 
>> have 
>> at regular quadrature points, via FEValues. 
>>
>> Best 
>> W. 
>>
>> -- 
>>  
>> Wolfgang Bangerth email: bang...@colostate.edu 
>> www: http://www.math.colostate.edu/~bangerth/ 
>>
>>
>>

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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-31 Thread Najwa Alshehri

Dear Wolfgang,

Thank you for your answer. I will try to write a patch to the deal.II 
sources that implement the missing function. This might require some time. 
I will come back here if needed.


Thank you all for your quick answers,
Najwa

On Wednesday, July 26, 2023 at 11:41:15 PM UTC+3 Wolfgang Bangerth wrote:

> On 7/26/23 12:17, Najwa Alshehri wrote:
> > 
> > Regarding the function "VectorFucntionFromScalarFunctionObject," I have 
> > observed that it works for computing the L2 norm of the error. However, 
> when I 
> > attempted to compute the H1_seminorm of the error, I noticed that the 
> gradient 
> > was not implemented for this function. Please let me know if my 
> understanding 
> > is incorrect, as I referred to the  for this.
>
> Yes, correct. Someone needs to implement
> VectorFucntionFromScalarFunctionObject::gradient()
> and/or
> VectorFucntionFromScalarFunctionObject::gradient_list()
> in exactly the same way as the value() and value_list() functions are 
> implemented.
>
>
> > Could you kindly advise me on the simplest way to accomplish this?
>
> The easiest way is to create a class derived from 
> VectorFucntionFromScalarFunctionObject in your own project that implements 
> the 
> missing function. The better way is to write a patch to the deal.II 
> sources 
> that implements the missing function because then others can use your work 
> in 
> the future as well :-)
>
>
> > On a side note, although "VectorFucntionFromScalarFunctionObject" works 
> with 
> > the L2 norm of the error, it is quite computationally intensive.
>
> It isn't VectorFucntionFromScalarFunctionObject that's expensive, but the 
> FEFieldFunction. That's sort of inherently the case with this class. If 
> you 
> can, it should be avoided and you should try an evaluate the FE field you 
> have 
> at regular quadrature points, via FEValues.
>
> Best
> W.
>
> -- 
> 
> Wolfgang Bangerth email: bang...@colostate.edu
> www: http://www.math.colostate.edu/~bangerth/
>
>
>

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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-26 Thread Wolfgang Bangerth


On 7/26/23 12:17, Najwa Alshehri wrote:


Regarding the function "VectorFucntionFromScalarFunctionObject," I have 
observed that it works for computing the L2 norm of the error. However, when I 
attempted to compute the H1_seminorm of the error, I noticed that the gradient 
was not implemented for this function. Please let me know if my understanding 
is incorrect, as I referred to the  for this.


Yes, correct. Someone needs to implement
  VectorFucntionFromScalarFunctionObject::gradient()
and/or
  VectorFucntionFromScalarFunctionObject::gradient_list()
in exactly the same way as the value() and value_list() functions are 
implemented.



Could you kindly advise me on the simplest way to accomplish this?


The easiest way is to create a class derived from 
VectorFucntionFromScalarFunctionObject in your own project that implements the 
missing function. The better way is to write a patch to the deal.II sources 
that implements the missing function because then others can use your work in 
the future as well :-)



On a side note, although "VectorFucntionFromScalarFunctionObject" works with 
the L2 norm of the error, it is quite computationally intensive.


It isn't VectorFucntionFromScalarFunctionObject that's expensive, but the 
FEFieldFunction. That's sort of inherently the case with this class. If you 
can, it should be avoided and you should try an evaluate the FE field you have 
at regular quadrature points, via FEValues.


Best
 W.

--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/


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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-26 Thread Najwa Alshehri

Greetings everyone,

I want to express my gratitude for your assistance with my question, which 
has evolved into something more profound.

Regarding the function "VectorFucntionFromScalarFunctionObject," I have 
observed that it works for computing the L2 norm of the error. However, 
when I attempted to compute the H1_seminorm of the error, I noticed that 
the gradient was not implemented for this function. Please let me know if 
my understanding is incorrect, as I referred to the 
 for this.

I am curious if there is a way to resolve this issue. My idea is to obtain 
the gradient of the "FeFeildFunction" since I know that the gradient is 
implemented for this function, as per 
. Afterward, I can define a new 
function within a class, based on "VectorFucntionFromScalarFunctionObject," 
where the gradient of that function would be the gradient of the 
"FeFeildFunction."

Could you kindly advise me on the simplest way to accomplish this? 

On a side note, although "VectorFucntionFromScalarFunctionObject" works 
with the L2 norm of the error, it is quite computationally intensive.

Best regards,
Najwa
On Sunday, July 23, 2023 at 4:47:50 PM UTC+3 Najwa Alshehri wrote:

> Dear Luca,
>
> This is interesting. I am exited to try this out. 
>
> Thank you so much,
> Najwa
>
> On Sunday, July 23, 2023 at 3:39:05 PM UTC+3 luca@gmail.com wrote:
>
>> FEFieldFunction has the same number of components of the underlying 
>> dofhandler. If that has one component, then so does the FEFieldFunction. 
>> What you could do is wrap the FEFieldFunction into another function, e.g.
>>
>> The deal.II Library: VectorFunctionFromScalarFunctionObject< dim, 
>> RangeNumberType > Class Template Reference 
>> 
>> dealii.org 
>> 
>> [image: deal.ico] 
>> 
>>  
>> 
>>
>> You could pass a lambda function as an argument to the constructor of the 
>> function, that uses your FEFieldFunction object, I.e.,
>>
>> VectorFucntionFromScalarFuncObj my_fun([&](const auto ){ return 
>> fe_field_func.value(p);}, 0, 2);
>>
>> Luca
>>
>> Il giorno 21 lug 2023, alle ore 22:05, Najwa Alshehri <
>> najwaa...@gmail.com> ha scritto:
>>
>> Dear Daniel, your answer makes sense, Finally it worked.
>>
>>
>> Dear Luca, thank you for your answer. Indeed, the ExactSolution is a 
>> class I built myself. I followed your suggestion and it was the magic line 
>> that solved the issue. *However,* say that I have in another code 
>> instead of using a ExactSolution that I build myself, I used an 
>> FeFieldFunction for a reference solution, how would I make this function 
>> allocate two components?
>>
>> Best,
>> Najwa
>>
>> On Friday, July 21, 2023 at 1:54:42 PM UTC+3 luca@gmail.com wrote:
>>
>>> Dear Najwa, 
>>>
>>> how many components do the `ExactSolution2` function has? 
>>>
>>> The error complains about `exact_solution.n_components, n_components` 
>>> not being equal, in particular it tells you that `ExactSolution2` only 
>>> has one component. 
>>>
>>> If you built the ExactSolution class yourself, make sure at construction 
>>> time you tell Function to allocate two components: 
>>>
>>> ExactSolution2::ExactSolution2( … ) 
>>> : Functions::Function(2) 
>>>
>>> Best, 
>>> Luca. 
>>>
>>>
>>> > On 20 Jul 2023, at 12:15, Najwa Alshehri  wrote: 
>>> > 
>>> > Hello again, 
>>> > 
>>> > I have a follow-up question. Does this ComponentSelectFunction work 
>>> also with vectors that are not written as blocked vectors? I have applied 
>>> it before when I was dealing with blocked vectors and it worked perfectly. 
>>> > 
>>> > So, I did this, 
>>> > const ComponentSelectFunction primal_mask(0,2); 
>>> > Later, 
>>> > VectorTools::integrate_difference(omega2_dh, 
>>> > u_omega2, 
>>> > ExactSolution2(), 
>>> > cellwise_errors2, 
>>> > quadrature, 
>>> > VectorTools::L2_norm 
>>> > ,_mask); 
>>> > const double u2_l2_error = 
>>> > VectorTools::compute_global_error(triangulation_omega2, 
>>> > cellwise_errors2, 
>>> > VectorTools::L2_norm); 
>>> > 
>>> > And I got the following error!! 
>>> > An error occurred in line <455> of file 
>>> <../include/deal.II/numerics/vector_tools_integrate_difference.templates.h> 
>>> in function 
>>> > void dealii::VectorTools::internal::do_integrate_difference(const 
>>> dealii::hp::MappingCollection&, const 
>>> dealii::DoFHandler&, const InVector&, const 
>>> dealii::Function&, OutVector&, 
>>> const dealii::hp::QCollection&, const dealii::VectorTools::NormType&, 
>>> const dealii::Function*, double) [with int dim = 2; int spacedim 
>>> = 2; InVector = dealii::Vector; OutVector = dealii::Vector; 
>>> typename InVector::value_type = double] 
>>> > The

Re: [deal.II] Q: Question about extracting part of a vector

2023-07-23 Thread Najwa Alshehri

Dear Luca,

This is interesting. I am exited to try this out. 

Thank you so much,
Najwa

On Sunday, July 23, 2023 at 3:39:05 PM UTC+3 luca@gmail.com wrote:

> FEFieldFunction has the same number of components of the underlying 
> dofhandler. If that has one component, then so does the FEFieldFunction. 
> What you could do is wrap the FEFieldFunction into another function, e.g.
>
> The deal.II Library: VectorFunctionFromScalarFunctionObject< dim, 
> RangeNumberType > Class Template Reference 
> 
> dealii.org 
> 
> [image: deal.ico] 
> 
>  
> 
>
> You could pass a lambda function as an argument to the constructor of the 
> function, that uses your FEFieldFunction object, I.e.,
>
> VectorFucntionFromScalarFuncObj my_fun([&](const auto ){ return 
> fe_field_func.value(p);}, 0, 2);
>
> Luca
>
> Il giorno 21 lug 2023, alle ore 22:05, Najwa Alshehri  
> ha scritto:
>
> Dear Daniel, your answer makes sense, Finally it worked.
>
>
> Dear Luca, thank you for your answer. Indeed, the ExactSolution is a class 
> I built myself. I followed your suggestion and it was the magic line that 
> solved the issue. *However,* say that I have in another code instead of 
> using a ExactSolution that I build myself, I used an FeFieldFunction for a 
> reference solution, how would I make this function allocate two components?
>
> Best,
> Najwa
>
> On Friday, July 21, 2023 at 1:54:42 PM UTC+3 luca@gmail.com wrote:
>
>> Dear Najwa, 
>>
>> how many components do the `ExactSolution2` function has? 
>>
>> The error complains about `exact_solution.n_components, n_components` not 
>> being equal, in particular it tells you that `ExactSolution2` only has 
>> one component. 
>>
>> If you built the ExactSolution class yourself, make sure at construction 
>> time you tell Function to allocate two components: 
>>
>> ExactSolution2::ExactSolution2( … ) 
>> : Functions::Function(2) 
>>
>> Best, 
>> Luca. 
>>
>>
>> > On 20 Jul 2023, at 12:15, Najwa Alshehri  wrote: 
>> > 
>> > Hello again, 
>> > 
>> > I have a follow-up question. Does this ComponentSelectFunction work 
>> also with vectors that are not written as blocked vectors? I have applied 
>> it before when I was dealing with blocked vectors and it worked perfectly. 
>> > 
>> > So, I did this, 
>> > const ComponentSelectFunction primal_mask(0,2); 
>> > Later, 
>> > VectorTools::integrate_difference(omega2_dh, 
>> > u_omega2, 
>> > ExactSolution2(), 
>> > cellwise_errors2, 
>> > quadrature, 
>> > VectorTools::L2_norm 
>> > ,_mask); 
>> > const double u2_l2_error = 
>> > VectorTools::compute_global_error(triangulation_omega2, 
>> > cellwise_errors2, 
>> > VectorTools::L2_norm); 
>> > 
>> > And I got the following error!! 
>> > An error occurred in line <455> of file 
>> <../include/deal.II/numerics/vector_tools_integrate_difference.templates.h> 
>> in function 
>> > void dealii::VectorTools::internal::do_integrate_difference(const 
>> dealii::hp::MappingCollection&, const 
>> dealii::DoFHandler&, const InVector&, const 
>> dealii::Function&, OutVector&, 
>> const dealii::hp::QCollection&, const dealii::VectorTools::NormType&, 
>> const dealii::Function*, double) [with int dim = 2; int spacedim 
>> = 2; InVector = dealii::Vector; OutVector = dealii::Vector; 
>> typename InVector::value_type = double] 
>> > The violated condition was: 
>> > 
>> ::dealii::deal_II_exceptions::internals::compare_for_equality(exact_solution.n_components,
>>  
>> n_components) 
>> > Additional information: 
>> > Dimension 1 not equal to 2. 
>> > 
>> > Obviously, we have dimensionality mismatching between u_omega2 and the 
>> exact solution. which means that the mask is not really picking up the 
>> first component of the solution u_omega2. Do you have any suggestions to 
>> fix this issue? 
>> > 
>> > Appreciate your help, 
>> > Najwa 
>> > On Thursday, July 20, 2023 at 11:48:04 AM UTC+3 Najwa Alshehri wrote: 
>> > Thank you Daniel for the clear quick answer. I will follow it. 
>> > 
>> > Best, 
>> > Najwa 
>> > 
>> > On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com 
>> wrote: 
>> > Najwa, 
>> > 
>> > The documentation of VectorTools::integrate_difference(
>> https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
>>  
>> says 
>> > 
>> > 
>> > The additional argument weight allows to evaluate weighted norms. The 
>> weight function may be scalar, establishing a spatially variable weight in 
>> the domain for all components equally. This may be used, for instance, to 
>> only integrate over parts of the domain. The weight function may also be 
>>

Re: [deal.II] Q: Question about extracting part of a vector

2023-07-23 Thread Luca Heltai

FEFieldFunction has the same number of components of the underlying dofhandler. If that has one component, then so does the FEFieldFunction. What you could do is wrap the FEFieldFunction into another function, e.g.The deal.II Library: VectorFunctionFromScalarFunctionObject< dim, RangeNumberType > Class Template Referencedealii.orgYou could pass a lambda function as an argument to the constructor of the function, that uses your FEFieldFunction object, I.e.,VectorFucntionFromScalarFuncObj my_fun([&](const auto ){ return fe_field_func.value(p);}, 0, 2);LucaIl giorno 21 lug 2023, alle ore 22:05, Najwa Alshehri  ha scritto:Dear Daniel, your answer makes sense, Finally it worked.Dear Luca, thank you for your answer. Indeed, the ExactSolution is a class I built myself. I followed your suggestion and it was the magic line that solved the issue. However, say that I have in another code instead of using a ExactSolution that I build myself, I used an FeFieldFunction for a reference solution, how would I make this function allocate two components?Best,NajwaOn Friday, July 21, 2023 at 1:54:42 PM UTC+3 luca@gmail.com wrote:Dear Najwa,

how many components do the `ExactSolution2` function has?

The error complains about `exact_solution.n_components, n_components` not being equal, in particular it tells you that `ExactSolution2` only has one component. 

If you built the ExactSolution class yourself, make sure at construction time you tell Function to allocate two components:

ExactSolution2::ExactSolution2( … ) 
   : Functions::Function(2)

Best,
Luca.

> On 20 Jul 2023, at 12:15, Najwa Alshehri  wrote:
> 
> Hello again,
> 
> I have a follow-up question. Does this ComponentSelectFunction work also with vectors that are not written as blocked vectors? I have applied it before when I was dealing with blocked vectors and it worked perfectly. 
> 
> So, I did this, 
> const ComponentSelectFunction primal_mask(0,2);
> Later,
> VectorTools::integrate_difference(omega2_dh,
> u_omega2,
> ExactSolution2(),
> cellwise_errors2,
> quadrature,
> VectorTools::L2_norm
> ,_mask);
> const double u2_l2_error =
> VectorTools::compute_global_error(triangulation_omega2,
> cellwise_errors2,
> VectorTools::L2_norm);
> 
> And I got the following error!!
> An error occurred in line <455> of file <../include/deal.II/numerics/vector_tools_integrate_difference.templates.h> in function
> void dealii::VectorTools::internal::do_integrate_difference(const dealii::hp::MappingCollection&, const dealii::DoFHandler&, const InVector&, const dealii::Function&, OutVector&, const dealii::hp::QCollection&, const dealii::VectorTools::NormType&, const dealii::Function*, double) [with int dim = 2; int spacedim = 2; InVector = dealii::Vector; OutVector = dealii::Vector; typename InVector::value_type = double]
> The violated condition was: 
> ::dealii::deal_II_exceptions::internals::compare_for_equality(exact_solution.n_components, n_components)
> Additional information: 
> Dimension 1 not equal to 2.
> 
>  Obviously, we have dimensionality mismatching between u_omega2 and the exact solution. which means that the mask is not really picking up the first component of the solution u_omega2.  Do you have any suggestions to fix this issue?
> 
> Appreciate your help,
> Najwa
> On Thursday, July 20, 2023 at 11:48:04 AM UTC+3 Najwa Alshehri wrote:
> Thank you Daniel for the clear quick answer. I will follow it.
> 
> Best,
> Najwa
> 
> On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com wrote:
> Najwa,
> 
> The documentation of VectorTools::integrate_difference(https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832) says
> 
> 
> The additional argument weight allows to evaluate weighted norms. The weight function may be scalar, establishing a spatially variable weight in the domain for all components equally. This may be used, for instance, to only integrate over parts of the domain. The weight function may also be vector-valued, with as many components as the finite element: Then, different components get different weights. A typical application is when the error with respect to only one or a subset of the solution variables is to be computed, in which case the other components would have weight values equal to zero. The ComponentSelectFunction class is particularly useful for this purpose as it provides such a "mask" weight. The weight function is expected to be positive, but negative values are not filtered. The default value of this function, a null pointer, is interpreted as "no weighting function", i.e., weight=1 in the whole domain for all vector components uniformly.
> 
> Best,
> Daniel
> 
> On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri  wrote:
> Dear group members,
> 
> I have one question, 
> 
> I am trying to calculate the L2 norm of the error of a solution. In particular, I have a vector of the solution u_omega and a FeSystem with two

Re: [deal.II] Q: Question about extracting part of a vector

2023-07-21 Thread Najwa Alshehri

Dear Daniel, your answer makes sense, Finally it worked.

Dear Luca, thank you for your answer. Indeed, the ExactSolution is a class 
I built myself. I followed your suggestion and it was the magic line that 
solved the issue. *However,* say that I have in another code instead of 
using a ExactSolution that I build myself, I used an FeFieldFunction for a 
reference solution, how would I make this function allocate two components?

Best,
Najwa

On Friday, July 21, 2023 at 1:54:42 PM UTC+3 luca@gmail.com wrote:

> Dear Najwa,
>
> how many components do the `ExactSolution2` function has?
>
> The error complains about `exact_solution.n_components, n_components` not 
> being equal, in particular it tells you that `ExactSolution2` only has 
> one component. 
>
> If you built the ExactSolution class yourself, make sure at construction 
> time you tell Function to allocate two components:
>
> ExactSolution2::ExactSolution2( … ) 
> : Functions::Function(2)
>
> Best,
> Luca.
>
>
> > On 20 Jul 2023, at 12:15, Najwa Alshehri  wrote:
> > 
> > Hello again,
> > 
> > I have a follow-up question. Does this ComponentSelectFunction work also 
> with vectors that are not written as blocked vectors? I have applied it 
> before when I was dealing with blocked vectors and it worked perfectly. 
> > 
> > So, I did this, 
> > const ComponentSelectFunction primal_mask(0,2);
> > Later,
> > VectorTools::integrate_difference(omega2_dh,
> > u_omega2,
> > ExactSolution2(),
> > cellwise_errors2,
> > quadrature,
> > VectorTools::L2_norm
> > ,_mask);
> > const double u2_l2_error =
> > VectorTools::compute_global_error(triangulation_omega2,
> > cellwise_errors2,
> > VectorTools::L2_norm);
> > 
> > And I got the following error!!
> > An error occurred in line <455> of file 
> <../include/deal.II/numerics/vector_tools_integrate_difference.templates.h> 
> in function
> > void dealii::VectorTools::internal::do_integrate_difference(const 
> dealii::hp::MappingCollection&, const 
> dealii::DoFHandler&, const InVector&, const 
> dealii::Function&, OutVector&, 
> const dealii::hp::QCollection&, const dealii::VectorTools::NormType&, 
> const dealii::Function*, double) [with int dim = 2; int spacedim 
> = 2; InVector = dealii::Vector; OutVector = dealii::Vector; 
> typename InVector::value_type = double]
> > The violated condition was: 
> > 
> ::dealii::deal_II_exceptions::internals::compare_for_equality(exact_solution.n_components,
>  
> n_components)
> > Additional information: 
> > Dimension 1 not equal to 2.
> > 
> > Obviously, we have dimensionality mismatching between u_omega2 and the 
> exact solution. which means that the mask is not really picking up the 
> first component of the solution u_omega2. Do you have any suggestions to 
> fix this issue?
> > 
> > Appreciate your help,
> > Najwa
> > On Thursday, July 20, 2023 at 11:48:04 AM UTC+3 Najwa Alshehri wrote:
> > Thank you Daniel for the clear quick answer. I will follow it.
> > 
> > Best,
> > Najwa
> > 
> > On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com 
> wrote:
> > Najwa,
> > 
> > The documentation of VectorTools::integrate_difference(
> https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
>  
> says
> > 
> > 
> > The additional argument weight allows to evaluate weighted norms. The 
> weight function may be scalar, establishing a spatially variable weight in 
> the domain for all components equally. This may be used, for instance, to 
> only integrate over parts of the domain. The weight function may also be 
> vector-valued, with as many components as the finite element: Then, 
> different components get different weights. A typical application is when 
> the error with respect to only one or a subset of the solution variables is 
> to be computed, in which case the other components would have weight values 
> equal to zero. The ComponentSelectFunction class is particularly useful for 
> this purpose as it provides such a "mask" weight. The weight function is 
> expected to be positive, but negative values are not filtered. The default 
> value of this function, a null pointer, is interpreted as "no weighting 
> function", i.e., weight=1 in the whole domain for all vector components 
> uniformly.
> > 
> > Best,
> > Daniel
> > 
> > On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri  
> wrote:
> > Dear group members,
> > 
> > I have one question, 
> > 
> > I am trying to calculate the L2 norm of the error of a solution. In 
> particular, I have a vector of the solution u_omega and a FeSystem with two 
> fes.
> > I am interested in computing the L2 norm of the error related to the 
> first fe using integrate_difference function. (Note here u_omega is not a 
> blocked vector, however, it has two solutions stacked together in one 
> vector). Can I extract the solution of the first part from u_omega?
> > 
> > 
> > Thank you in advance for your help.
> > Best,
> > Najwa
> > 
> > -- 
> > The deal.II project is located

Re: [deal.II] Q: Question about extracting part of a vector

2023-07-20 Thread Daniel Arndt

Najwa,

the relevant code reads something like

  const unsigned int n_components = dof.get_fe(0).n_components();
  AssertDimension(exact_solution.n_components, n_components);
  if (weight != nullptr)
{
  Assert((weight->n_components == 1) ||
   (weight->n_components == n_components),
 ExcDimensionMismatch(weight->n_components, n_components));
}

which means that your exact solution still needs to have as many components
as the FiniteElement object used (and the number of components for
ComponentSelectFunction must also match that).
ComponentSelectFunction then makes sure that all other components are
ignored when computing the error.

Best,
Daniel

On Thu, Jul 20, 2023 at 6:15 AM Najwa Alshehri 
wrote:

> Hello again,
>
> I have a follow-up question. Does this ComponentSelectFunction work also
> with vectors that are not written as blocked vectors? I have applied it
> before when I was dealing with blocked vectors and it worked perfectly.
>
> So, I did this,
> const ComponentSelectFunction primal_mask(0,2);
> Later,
> VectorTools::integrate_difference(omega2_dh,
> u_omega2,
> ExactSolution2(),
> cellwise_errors2,
> quadrature,
> VectorTools::L2_norm
> ,_mask);
> const double u2_l2_error =
> VectorTools::compute_global_error(triangulation_omega2,
> cellwise_errors2,
> VectorTools::L2_norm);
>
> And I got the following error!!
> An error occurred in line <455> of file
> <../include/deal.II/numerics/vector_tools_integrate_difference.templates.h>
> in function
> void dealii::VectorTools::internal::do_integrate_difference(const
> dealii::hp::MappingCollection&, const
> dealii::DoFHandler&, const InVector&, const
> dealii::Function&, OutVector&,
> const dealii::hp::QCollection&, const dealii::VectorTools::NormType&,
> const dealii::Function*, double) [with int dim = 2; int spacedim
> = 2; InVector = dealii::Vector; OutVector = dealii::Vector;
> typename InVector::value_type = double]
> The violated condition was:
>
> ::dealii::deal_II_exceptions::internals::compare_for_equality(exact_solution.n_components,
> n_components)
> Additional information:
> Dimension 1 not equal to 2.
>
>  Obviously, we have dimensionality mismatching between u_omega2 and the
> exact solution. which means that the mask is not really picking up the
> first component of the solution u_omega2.  Do you have any suggestions to
> fix this issue?
>
> Appreciate your help,
> Najwa
> On Thursday, July 20, 2023 at 11:48:04 AM UTC+3 Najwa Alshehri wrote:
>
>> Thank you Daniel for the clear quick answer. I will follow it.
>>
>> Best,
>> Najwa
>>
>> On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com
>> wrote:
>>
>>> Najwa,
>>>
>>> The documentation of VectorTools::integrate_difference(
>>> https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
>>> says
>>>
>>>
>>> The additional argument weight allows to evaluate weighted norms. The
>>> weight function may be scalar, establishing a spatially variable weight in
>>> the domain for all components equally. This may be used, for instance, to
>>> only integrate over parts of the domain. The weight function may also be
>>> vector-valued, with as many components as the finite element: Then,
>>> different components get different weights. A typical application is when
>>> the error with respect to only one or a subset of the solution variables is
>>> to be computed, in which case the other components would have weight values
>>> equal to zero. The ComponentSelectFunction
>>> 
>>> class is particularly useful for this purpose as it provides such a "mask"
>>> weight. The weight function is expected to be positive, but negative values
>>> are not filtered. The default value of this function, a null pointer, is
>>> interpreted as "no weighting function", i.e., weight=1 in the whole domain
>>> for all vector components uniformly.
>>>
>>> Best,
>>> Daniel
>>>
>>> On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri 
>>> wrote:
>>>
 Dear group members,

 I have one question,

 I am trying to calculate the L2 norm of the error of a solution. In
 particular, I have a *vector of the solution* u_omega and a *FeSystem*
 with two fes.

 I am interested in computing the L2 norm of the error related to the
 first fe using *integrate_difference * function. (Note here u_omega is *not
 a blocked vector*, however, it has two solutions stacked together in
 one vector). Can I extract the solution of the first part from u_omega?



 Thank you in advance for your help.

 Best,

 Najwa

 --
 The deal.II project is located at http://www.dealii.org/
 For mailing list/forum options, see
 https://groups.google.com/d/forum/dealii?hl=en
 ---
 You received this message because you are subscribed to the Google

Re: [deal.II] Q: Question about extracting part of a vector

2023-07-20 Thread Najwa Alshehri

Hello again,

I have a follow-up question. Does this ComponentSelectFunction work also 
with vectors that are not written as blocked vectors? I have applied it 
before when I was dealing with blocked vectors and it worked perfectly. 

So, I did this, 
const ComponentSelectFunction primal_mask(0,2);
Later,
VectorTools::integrate_difference(omega2_dh,
u_omega2,
ExactSolution2(),
cellwise_errors2,
quadrature,
VectorTools::L2_norm
,_mask);
const double u2_l2_error =
VectorTools::compute_global_error(triangulation_omega2,
cellwise_errors2,
VectorTools::L2_norm);

And I got the following error!!
An error occurred in line <455> of file 
<../include/deal.II/numerics/vector_tools_integrate_difference.templates.h> 
in function
void dealii::VectorTools::internal::do_integrate_difference(const 
dealii::hp::MappingCollection&, const 
dealii::DoFHandler&, const InVector&, const 
dealii::Function&, OutVector&, 
const dealii::hp::QCollection&, const dealii::VectorTools::NormType&, 
const dealii::Function*, double) [with int dim = 2; int spacedim 
= 2; InVector = dealii::Vector; OutVector = dealii::Vector; 
typename InVector::value_type = double]
The violated condition was: 

::dealii::deal_II_exceptions::internals::compare_for_equality(exact_solution.n_components,
 
n_components)
Additional information: 
Dimension 1 not equal to 2.

 Obviously, we have dimensionality mismatching between u_omega2 and the 
exact solution. which means that the mask is not really picking up the 
first component of the solution u_omega2.  Do you have any suggestions to 
fix this issue?

Appreciate your help,
Najwa
On Thursday, July 20, 2023 at 11:48:04 AM UTC+3 Najwa Alshehri wrote:

> Thank you Daniel for the clear quick answer. I will follow it.
>
> Best,
> Najwa
>
> On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com wrote:
>
>> Najwa,
>>
>> The documentation of VectorTools::integrate_difference(
>> https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
>>  
>> says
>>
>>
>> The additional argument weight allows to evaluate weighted norms. The 
>> weight function may be scalar, establishing a spatially variable weight in 
>> the domain for all components equally. This may be used, for instance, to 
>> only integrate over parts of the domain. The weight function may also be 
>> vector-valued, with as many components as the finite element: Then, 
>> different components get different weights. A typical application is when 
>> the error with respect to only one or a subset of the solution variables is 
>> to be computed, in which case the other components would have weight values 
>> equal to zero. The ComponentSelectFunction 
>> 
>>  
>> class is particularly useful for this purpose as it provides such a "mask" 
>> weight. The weight function is expected to be positive, but negative values 
>> are not filtered. The default value of this function, a null pointer, is 
>> interpreted as "no weighting function", i.e., weight=1 in the whole domain 
>> for all vector components uniformly.
>>
>> Best,
>> Daniel
>>
>> On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri  
>> wrote:
>>
>>> Dear group members,
>>>
>>> I have one question, 
>>>
>>> I am trying to calculate the L2 norm of the error of a solution. In 
>>> particular, I have a *vector of the solution* u_omega and a *FeSystem* 
>>> with two fes.
>>>
>>> I am interested in computing the L2 norm of the error related to the 
>>> first fe using *integrate_difference * function. (Note here u_omega is *not 
>>> a blocked vector*, however, it has two solutions stacked together in 
>>> one vector). Can I extract the solution of the first part from u_omega?
>>>
>>>
>>>
>>> Thank you in advance for your help.
>>>
>>> Best,
>>>
>>> Najwa
>>>
>>> -- 
>>> The deal.II project is located at http://www.dealii.org/
>>> For mailing list/forum options, see 
>>> https://groups.google.com/d/forum/dealii?hl=en
>>> --- 
>>> You received this message because you are subscribed to the Google 
>>> Groups "deal.II User Group" group.
>>> To unsubscribe from this group and stop receiving emails from it, send 
>>> an email to dealii+un...@googlegroups.com.
>>> To view this discussion on the web visit 
>>> https://groups.google.com/d/msgid/dealii/9741338e-2a31-418b-815d-277a5d7cb573n%40googlegroups.com
>>>  
>>> 
>>> .
>>>
>>

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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-20 Thread Najwa Alshehri

Thank you Daniel for the clear quick answer. I will follow it.

Best,
Najwa

On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com wrote:

> Najwa,
>
> The documentation of VectorTools::integrate_difference(
> https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
>  
> says
>
>
> The additional argument weight allows to evaluate weighted norms. The 
> weight function may be scalar, establishing a spatially variable weight in 
> the domain for all components equally. This may be used, for instance, to 
> only integrate over parts of the domain. The weight function may also be 
> vector-valued, with as many components as the finite element: Then, 
> different components get different weights. A typical application is when 
> the error with respect to only one or a subset of the solution variables is 
> to be computed, in which case the other components would have weight values 
> equal to zero. The ComponentSelectFunction 
> 
>  
> class is particularly useful for this purpose as it provides such a "mask" 
> weight. The weight function is expected to be positive, but negative values 
> are not filtered. The default value of this function, a null pointer, is 
> interpreted as "no weighting function", i.e., weight=1 in the whole domain 
> for all vector components uniformly.
>
> Best,
> Daniel
>
> On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri  
> wrote:
>
>> Dear group members,
>>
>> I have one question, 
>>
>> I am trying to calculate the L2 norm of the error of a solution. In 
>> particular, I have a *vector of the solution* u_omega and a *FeSystem* 
>> with two fes.
>>
>> I am interested in computing the L2 norm of the error related to the 
>> first fe using *integrate_difference * function. (Note here u_omega is *not 
>> a blocked vector*, however, it has two solutions stacked together in one 
>> vector). Can I extract the solution of the first part from u_omega?
>>
>>
>>
>> Thank you in advance for your help.
>>
>> Best,
>>
>> Najwa
>>
>> -- 
>> The deal.II project is located at http://www.dealii.org/
>> For mailing list/forum options, see 
>> https://groups.google.com/d/forum/dealii?hl=en
>> --- 
>> You received this message because you are subscribed to the Google Groups 
>> "deal.II User Group" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
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>> https://groups.google.com/d/msgid/dealii/9741338e-2a31-418b-815d-277a5d7cb573n%40googlegroups.com
>>  
>> 
>> .
>>
>

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Re: [deal.II] Q: Question about extracting part of a vector

2023-07-19 Thread Daniel Arndt

Najwa,

The documentation of VectorTools::integrate_difference(
https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
says

The additional argument weight allows to evaluate weighted norms. The
weight function may be scalar, establishing a spatially variable weight in
the domain for all components equally. This may be used, for instance, to
only integrate over parts of the domain. The weight function may also be
vector-valued, with as many components as the finite element: Then,
different components get different weights. A typical application is when
the error with respect to only one or a subset of the solution variables is
to be computed, in which case the other components would have weight values
equal to zero. The ComponentSelectFunction

class is particularly useful for this purpose as it provides such a "mask"
weight. The weight function is expected to be positive, but negative values
are not filtered. The default value of this function, a null pointer, is
interpreted as "no weighting function", i.e., weight=1 in the whole domain
for all vector components uniformly.

Best,
Daniel

On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri 
wrote:

> Dear group members,
>
> I have one question,
>
> I am trying to calculate the L2 norm of the error of a solution. In
> particular, I have a *vector of the solution* u_omega and a *FeSystem*
> with two fes.
>
> I am interested in computing the L2 norm of the error related to the first
> fe using *integrate_difference * function. (Note here u_omega is *not a
> blocked vector*, however, it has two solutions stacked together in one
> vector). Can I extract the solution of the first part from u_omega?
>
>
>
> Thank you in advance for your help.
>
> Best,
>
> Najwa
>
> --
> The deal.II project is located at http://www.dealii.org/
> For mailing list/forum options, see
> https://groups.google.com/d/forum/dealii?hl=en
> ---
> You received this message because you are subscribed to the Google Groups
> "deal.II User Group" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to dealii+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/dealii/9741338e-2a31-418b-815d-277a5d7cb573n%40googlegroups.com
> 
> .
>

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[deal.II] Q: Question about extracting part of a vector

2023-07-19 Thread Najwa Alshehri

Dear group members,

I have one question, 

I am trying to calculate the L2 norm of the error of a solution. In 
particular, I have a *vector of the solution* u_omega and a *FeSystem* with 
two fes.

I am interested in computing the L2 norm of the error related to the first 
fe using *integrate_difference * function. (Note here u_omega is *not a 
blocked vector*, however, it has two solutions stacked together in one 
vector). Can I extract the solution of the first part from u_omega?



Thank you in advance for your help.

Best,

Najwa

-- 
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https://groups.google.com/d/forum/dealii?hl=en
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[deal.II] Q: Question about extracting part of a vector

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