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GNU Scientific Library determinant of complex array help

by tosburn3
Tags: array, complex, determinant, library, scientific
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tosburn3
#1
Mar15-12, 05:26 PM
P: 6
So I suck at programming, but I need to find the determinant of a complex 6x6 array using GSL in C (not GSL complex, complex.h complex). Here is what has failed so far starting with a 6x6 double complex array named mymatrix:

gsl_matrix_complex_view m = gsl_matrix_complex_view_array(mymatrix, 6, 6);
int s;
gsl_permutation *p = gsl_permutation_alloc(6);
gsl_linalg_complex_LU_decomp(&m.matrix, p, &s);
gsl_complex det2 = gsl_linalg_complex_LU_det(&m.matrix, s);
double complex det1 = GSL_REAL(det2)+I*GSL_IMAG(det2);

I refuse to convert my entire program to GSL's complex stuff if you think that would fix it. Here is the error message when compiling in gcc:

lorenz_odd_1.c: In function ‘det’:
lorenz_odd_1.c:122:1: warning: passing argument 1 of ‘gsl_matrix_complex_view_array’ from incompatible pointer type
/usr/local/include/gsl/gsl_matrix_complex_double.h:128:1: note: expected ‘double *’ but argument is of type ‘__complex__ double *’
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I like Serena
#2
Mar15-12, 06:23 PM
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Welcome to PF, tosburn3!

To make any function of GSL work with complex numbers, you need to convert your complex numbers to GSL complex stuff.

Yeah... so I'm suggesting that one.
Sorry.
tosburn3
#3
Mar15-12, 06:54 PM
P: 6
Quote Quote by I like Serena View Post
Welcome to PF, tosburn3!

To make any function of GSL work with complex numbers, you need to convert your complex numbers to GSL complex stuff.

Yeah... so I'm suggesting that one.
Sorry.
I don't care if I have to use GSL crap as intermediate steps. I just want to start with a regular complex array and end with a regular complex number. It was my understanding that:

gsl_matrix_complex_view m = gsl_matrix_complex_view_array(mymatrix, 6, 6);

Will take "mymatrix" and make a gsl_matrix_complex called "m", and then at the end I convert back to a regular complex number (quite inefficiently I might add).

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#4
Mar15-12, 06:59 PM
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GNU Scientific Library determinant of complex array help

It does not matter if it's inefficient.
In terms of performance, calculating a determinant is so much more computationally difficult, that a conversion of complex numbers matters not at all.
It's only a little more code.

But... what is your problem then?
tosburn3
#5
Mar15-12, 07:08 PM
P: 6
FWIW here is the error message when compiling with gcc (updated original post for recent version):

lorenz_odd_1.c: In function ‘det’:
lorenz_odd_1.c:122:1: warning: passing argument 1 of ‘gsl_matrix_complex_view_array’ from incompatible pointer type
/usr/local/include/gsl/gsl_matrix_complex_double.h:128:1: note: expected ‘double *’ but argument is of type ‘__complex__ double *’
tosburn3
#6
Mar15-12, 07:20 PM
P: 6
Quote Quote by I like Serena View Post
It does not matter if it's inefficient.
In terms of performance, calculating a determinant is so much more computationally difficult, that a conversion of complex numbers matters not at all.
It's only a little more code.

But... what is your problem then?
Also, the inefficiency was actually that I computed the determinant once for the real part then again for the imaginary part, which would in fact take a lot longer.
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#7
Mar15-12, 07:21 PM
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Oh okay, so your "mymatrix" is of the wrong type, apparently something like "double complex*".
How did you define "mymatrix"?

Anyway, I strongly recommend that you convert your mymatrix to the type gsl_matrix_complex_view_array() expects.
Just allocate the gsl matrix and fill it with 2 for-loops.
It really does not pay to try to make any shortcuts here.

Generally any shortcuts work against you.
If not now, then later.
tosburn3
#8
Mar15-12, 07:24 PM
P: 6
Quote Quote by I like Serena View Post
Oh okay, so your "mymatrix" is of the wrong type, apparently something like "double complex*".
How did you define "mymatrix"?

Anyway, I strongly recommend that you convert your mymatrix to the type gsl_matrix_complex_view_array() expects.
Just allocate the gsl matrix and fill it with 2 for-loops.
It really does not pay to try to make any shortcuts here.

Generally any shortcuts work against you.
If not now, then later.
mymatrix is in fact a double complex. I will try that.
tosburn3
#9
Mar15-12, 07:59 PM
P: 6
While I'm still not sure why the other way didn't work, looping through each component seems to work. At least it compiles...

Thanks!
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#10
Mar15-12, 08:16 PM
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Good!
AlephZero
#11
Mar15-12, 10:05 PM
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Thanks
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Alternatively you could use LAPACK, which will work on an ordinary Fortran array.


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