GNU Scientific Library determinant of complex array help

  • Thread starter tosburn3
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  • #1
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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 *’
 
Last edited:

Answers and Replies

  • #2
I like Serena
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Welcome to PF, tosburn3! :smile:

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.
 
  • #3
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Welcome to PF, tosburn3! :smile:

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).
 
  • #4
I like Serena
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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?
 
  • #5
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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 *’
 
  • #6
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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.
 
  • #7
I like Serena
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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.
 
  • #8
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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.

mymatrix is in fact a double complex. I will try that.
 
  • #9
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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!
 
  • #10
I like Serena
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Good! :wink:
 
  • #11
AlephZero
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Alternatively you could use LAPACK, which will work on an ordinary Fortran array.
 

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