Thanks Jean-Paul, To be honest I start thinking that starting this Coursera course was a mistake. The majority of the questions have no answer, people asking many times and no answer... that a pitty!, this assignment has already turned into something personal indeed XD. So far I have been able to exchange some mails with professor Garikipati but, otherwise my questions would simply left without answer in the course forum. It seems to me I am the only one following this course nowadays XD. anyway... I really appreaciate that you use some time to asnwer me :) actually I have other questions that I posted in the Coursera forum, I will give some time to Prof. Garikipati to answer but, looks that there should me some "course moderators", I do not understand it. If I do not get some answers from coursera could I ask you something else regarding this coding assignment? it is just I have some other doubts... anyway Jean-Paul, thank you in advance!
Jordi, On Friday, 3 January 2020 17:26:34 UTC-5, Jean-Paul Pelteret wrote: > > Hi Jordi, > > Well, Brandon actually provided you with the key phrase that I was hinting > towards. This element of the code looks in order for linear basis > functions. However, it looks to me like there's actually a set of comments > in your code that suggests/indicates that you’ve not completed something > that is relevant when using higher order basis functions. It is presumably > this that renders your system matrix non-invertible when using quadratic or > cubic basis functions, which is what UMFPack is complaining about when this > message (which I presume is the one that you see) is emitted > > $ make run > Scanning dependencies of target main1 > [ 33%] Building CXX object CMakeFiles/main1.dir/main1.cc.o > [ 66%] Linking CXX executable main1 > [ 66%] Built target main1 > [100%] Run main1 with Debug configuration > Number of active elems: 2 > Number of degrees of freedom: 5 > > > ---------------------------------------------------- > Exception on processing: > > -------------------------------------------------------- > An error occurred in line <291> of file > <path/dealii/source/lac/sparse_direct.cc> in function > void dealii::SparseDirectUMFPACK::factorize(const Matrix &) [Matrix = > dealii::SparseMatrix<double>] > The violated condition was: > status == UMFPACK_OK > Additional information: > UMFPACK routine umfpack_dl_numeric returned error status 1. > > A complete list of error codes can be found in the file > <bundled/umfpack/UMFPACK/Include/umfpack.h>. > > That said, the two most common errors that can happen are that your matrix > cannot be factorized because it is rank deficient, and that UMFPACK runs > out of memory because your problem is too large. > > The first of these cases most often happens if you forget terms in your > bilinear form necessary to ensure that the matrix has full rank, or if your > equation has a spatially variable coefficient (or nonlinearity) that is > supposed to be strictly positive but, for whatever reasons, is negative or > zero. In either case, you probably want to check your assembly procedure. > Similarly, a matrix can be rank deficient if you forgot to apply the > appropriate boundary conditions. For example, the Laplace equation without > boundary conditions has a single zero eigenvalue and its rank is therefore > deficient by one. > > The other common situation is that you run out of memory. On a typical > laptop or desktop, it should easily be possible to solve problems with > 100,000 unknowns in 2d. If you are solving problems with many more unknowns > than that, in particular if you are in 3d, then you may be running out of > memory and you will need to consider iterative solvers instead of the > direct solver employed by UMFPACK. > > You can also take a look at the first 8-10 paragraphs of this section of a > tutorial > https://dealii.org/current/doxygen/deal.II/step_3.html#Step3assemble_system > which may also give you some further insights into where (I think) you’re > going wrong. > > Good luck! > Jean-Paul > > On 03 Jan 2020, at 19:28, Jordi Parra Porcar <[email protected] > <javascript:>> wrote: > > Hello Jean-Paul, > > Thanks in advance for your time answering my question, unfortunately I > have been unable to understand what do you mean in your somewhat criptic > explanation :(. I was thinking about something wrong with the implication > of the Jacobian in the basis gradients but, for 1d and 2d this has not to > be affecting due to the same spacing between nodes. Can you somehow > "decript" your answer a little bit, I am really struggling with this > assignment XD > > Kind regards and thanks again! > > On Sunday, 29 December 2019 16:29:11 UTC-5, Jean-Paul Pelteret wrote: >> >> Dear Jordi, >> >> Firstly, welcome to the forum. Well, as this is a course assignment I >> think that its fair to assume that some course mentor should be available >> to guide you toward the solution to the problem. You say that you’ve had no >> luck on the course site forum — that’s a bit poor. Anyway, I wouldn’t want >> to give away the answer, but after skimming through your code and seeing >> your comment that >> >> I checked my basis functions and its gradients and seem to be correct >> >> >> I would say that you’re looking in the right sorts of places for the >> problem. Remember that in the finite element method we use basis functions >> to approximate the solution, and these need to evaluated in certain places >> where we form approximations for certain calculations. You’ve seem to have >> the “evaluated” part sorted, but what about the other part? What might need >> to change when you move from linear to higher order shape functions in >> order to ensure that those approximate calculations are performed >> accurately? >> >> I hope that my somewhat cryptic response will give you a nudge in the >> right direction. Oh, and I also hope that you take a look at our tutorial >> programs sometime to see how we typically code up FEM problems. It’s good >> to get a hand on the basics, but you might be pleased to know that the >> deal.II library does most of this for you in a clean and easy to understand >> manner. >> >> Best, >> Jean-Paul >> >> On 28 Dec 2019, at 02:01, Jordi Parra Porcar <[email protected]> >> wrote: >> >> Dear all, >> >> I am new to this group. I wanted to ask for some help as I am unable to >> find the solution to a problem. >> I am following a course in Coursera called "The Finite Element Method for >> problems in physics". The course first assignment it is about coding with >> dealii. >> I have posted in the Coursera forum but got no answer so, I am trying by >> here just to see if I am lucky and someone give me a hand. >> The issue that I have is that I can only solve the problem with 1st order >> basis functions as with quadratic and cubic basis functions it gives me an >> error related with the K global matrix. >> I have been going around discussions but still unable to find where is >> the problem. I checked my basis functions and its gradients and seem to be >> correct. >> I uploaded all the files related to the problem. Now the ./main executes >> the problem=1 with order=1, that is the linear basis function. >> >> Thank you all in advance and happy ending of the year! >> >> Jordi, >> >> -- >> 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 [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/dealii/5a12993f-9687-4b5a-9ad5-e4711e49f6a4%40googlegroups.com >> >> <https://groups.google.com/d/msgid/dealii/5a12993f-9687-4b5a-9ad5-e4711e49f6a4%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> <CMakeCache.txt><CMakeLists.txt><FEM1.h><Makefile><cmake_install.cmake> >> <main1><main1.cc><writeSolutions.h> >> <_b66323d90964cccb91c92f77bcb02ab0_codingAssign1.pdf> >> >> >> > -- > 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 [email protected] <javascript:>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/f7bfa8a0-6c68-4e91-bc48-7170f37f5934%40googlegroups.com > > <https://groups.google.com/d/msgid/dealii/f7bfa8a0-6c68-4e91-bc48-7170f37f5934%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > > -- 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. 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