Re: [Flightgear-devel] Arrays of doubles
On Fri, Apr 09, 2004 at 08:03:49AM -0500, Jon Berndt wrote: class. All I want right now is how do I allocate storage for a 2 dimensional array of doubles, so that I can use the standard accessor operators: myDouble = Data[n][m]; If you insist on the [][] syntax, I'd strongly recommend a std::vector std::vector double . If not, you can use one of the many C++ matrix implementations floating around, for example (shameless plug :-) cpp-lib, which is available from my homepage: http://www.cosy.sbg.ac.at/~gwesp/ Here you can access the elements by Data( n , m ) ( 1 = n = rows , 1 = m = columns ) (Similar to FORTRAN notation). Kind regards, -Gerhard -- Gerhard Wesp o o Tel.: +41 (0) 43 5347636 Bachtobelstrasse 56 | http://www.cosy.sbg.ac.at/~gwesp/ CH-8045 Zuerich \_/ See homepage for email address! ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
[Flightgear-devel] Arrays of doubles
Is there a better way to allocate storage for an array than this:
double** Allocate(void)
{
Data = new double*[nRows+1];
for (int r=0; r=nRows; r++) {
Data[r] = new double[nCols+1];
for (int c=0; c=nCols; c++) {
Data[r][c] = 0.0;
}
}
return Data;
}
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Re: [Flightgear-devel] Arrays of doubles
On Freitag, 9. April 2004 14:26, Jon Berndt wrote:
Is there a better way to allocate storage for an array than this:
double** Allocate(void)
{
Data = new double*[nRows+1];
for (int r=0; r=nRows; r++) {
Data[r] = new double[nCols+1];
for (int c=0; c=nCols; c++) {
Data[r][c] = 0.0;
}
}
return Data;
}
Depends on what you need.
If you really need an array of an array there is nothing I know of.
If you need a 2-dimensional/n-dimensional array for the upcomming
multidimensional lookup tables, you told about, I would suggest to allocate
the space in one block and implement access functions just like we did for
the Matrix class.
Greetings
Mathias
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RE: [Flightgear-devel] Arrays of doubles
On Freitag, 9. April 2004 14:26, Jon Berndt wrote:
Is there a better way to allocate storage for an array than this:
double** Allocate(void)
{
Data = new double*[nRows+1];
for (int r=0; r=nRows; r++) {
Data[r] = new double[nCols+1];
for (int c=0; c=nCols; c++) {
Data[r][c] = 0.0;
}
}
return Data;
}
Depends on what you need.
If you really need an array of an array there is nothing I know of.
If you need a 2-dimensional/n-dimensional array for the upcomming
multidimensional lookup tables, you told about, I would suggest
to allocate
the space in one block and implement access functions just like
we did for
the Matrix class.
I am afraid it is much simpler than that: all I need is a 2 dimensional
array, n X m.
Jon
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Re: [Flightgear-devel] Arrays of doubles
On Freitag, 9. April 2004 14:39, Jon Berndt wrote:
I am afraid it is much simpler than that: all I need is a 2 dimensional
array, n X m.
For such a simple array it is best to use
data = new double[n*m]
and have access functions:
double Entry(unsigned int i,unsigned int j) const { return
data[(i-1)*n+j-1]; }
double Entry(unsigned int i,unsigned int j) { return data[(i-1)*n+j-1]; }
Where the -1 terms are usually optimized away by the compiler.
Alternatively you can start indexing with 0 ...
For constants in the arguments to the Entry(..) function, this will be faster
than having an array of arrays, since the compiler can compute the offset to
the array pointer at compile time. If you have an array of arrays the
compiler needs to lookup array pointer in the first array and can then use
the precomputed offset.
For nonconst indices this kind of depends on the architecture and the
compiler ...
You will use more memory if you use this array of arrays ...
Greetings
Mathias
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RE: [Flightgear-devel] Arrays of doubles
For such a simple array it is best to use
data = new double[n*m]
and have access functions:
double Entry(unsigned int i,unsigned int j) const { return
data[(i-1)*n+j-1]; }
double Entry(unsigned int i,unsigned int j) { return data[(i-1)*n+j-1]; }
Yes, this may come at some time. I am debuggin the additions to the Table
class. All I want right now is how do I allocate storage for a 2
dimensional array of doubles, so that I can use the standard accessor
operators:
myDouble = Data[n][m];
??
Jon
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Re: [Flightgear-devel] Arrays of doubles
On Freitag, 9. April 2004 15:03, Jon Berndt wrote: I am debuggin the additions to the Table class. All I want right now is how do I allocate storage for a 2 dimensional array of doubles, so that I can use the standard accessor operators: myDouble = Data[n][m]; ?? Hmm, two possibilities. You are talking about FGTable, I think. Either you have to use the array of arrays solution. This is required in this case if the array *needs* to have a dynamic size. Alternatively I can see for this application and for debugging, depends on what you debug, that you declare double Data[one sufficieltly large number][an other sufficiently largenumber]; instead of double** Data; Using this you can just use the syntax from above to access the array members. As told, not for production, only for debuging ... So what is the problem? What do you need to debug? Greetings Mathias -- Mathias Fröhlich, email: [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] Arrays of doubles
I'll send you the problem offline. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Mathias Fröhlich Sent: Friday, April 09, 2004 8:16 AM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] Arrays of doubles On Freitag, 9. April 2004 15:03, Jon Berndt wrote: I am debuggin the additions to the Table class. All I want right now is how do I allocate storage for a 2 dimensional array of doubles, so that I can use the standard accessor operators: myDouble = Data[n][m]; ?? Hmm, two possibilities. You are talking about FGTable, I think. Either you have to use the array of arrays solution. This is required in this case if the array *needs* to have a dynamic size. Alternatively I can see for this application and for debugging, depends on what you debug, that you declare double Data[one sufficieltly large number][an other sufficiently largenumber]; instead of double** Data; Using this you can just use the syntax from above to access the array members. As told, not for production, only for debuging ... So what is the problem? What do you need to debug? Greetings Mathias -- Mathias Fröhlich, email: [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Arrays of doubles
On Freitag, 9. April 2004 15:31, Jon Berndt wrote: I'll send you the problem offline. Ok. Greetings Mathias -- Mathias Fröhlich, email: [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
