Compiling lapacke example code? - c++

Question

I'm trying to compile the examples found here:
http://www.netlib.org/lapack/lapacke.html#_examples
Specifically, I'm trying to get the "Calling CGEQRF and the CBLAS" example to work. The code is like so:
#include <stdio.h>
#include <stdlib.h>
#include <lapacke.h>
#include <cblas.h>
int main (int argc, const char * argv[])
{
lapack_complex_float *a,*tau,*r,one,zero;
lapack_int info,m,n,lda;
int i,j;
float err=0.0;
m = 10; n = 5; lda = m;
one = lapack_make_complex_float(1.0,0.0);
zero= lapack_make_complex_float(0.0,0.0);
a = calloc(m*n,sizeof(lapack_complex_float));
r = calloc(n*n,sizeof(lapack_complex_float));
tau = calloc(m,sizeof(lapack_complex_float));
for(j=0;j<n;j++)
for(i=0;i<m;i++)
a[i+j*m] = lapack_make_complex_float(i+1,j+1);
info = LAPACKE_cgeqrf(LAPACK_COL_MAJOR,m,n,a,lda,tau);
info = LAPACKE_cungqr(LAPACK_COL_MAJOR,m,n,n,a,lda,tau);
for(j=0;j<n;j++)
for(i=0;i<n;i++)
r[i+j*n]=(i==j)?-one:zero;
cblas_cgemm(CblasColMajor,CblasConjTrans,CblasNoTrans,
n,n,m,&one,a,lda,a,lda,&one,r,n );
for(i=0;i<n;i++)
for(j=0;j<n;j++)
err=MAX(err,cabs(r[i+j*n]));
printf("error=%e\n",err);
free(tau);
free(r);
free(a);
return(info);
}
If I save the file as a .cpp (perhaps this is my first mistake?) and compile using
g++ lapacketest.cpp -llapack
I get the following compile errors:
3_20_2.cpp:14:7: error: assigning to '_Complex float *' from incompatible type 'void *'
a = calloc(m*n,sizeof(lapack_complex_float));
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3_20_2.cpp:15:7: error: assigning to '_Complex float *' from incompatible type 'void *'
r = calloc(n*n,sizeof(lapack_complex_float));
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3_20_2.cpp:16:9: error: assigning to '_Complex float *' from incompatible type 'void *'
tau = calloc(m,sizeof(lapack_complex_float));
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3_20_2.cpp:29:25: error: use of undeclared identifier 'cabs'
err=MAX(err,cabs(r[i+j*n]));
I tried changing to .c and compiling with gcc, but I got other strange errors. Any thoughts? I'm slowly trying transition from Matlab to c++ for scientific computing and so far it's just been a giant headache.

Answer 1

It looks like calloc(m*n,sizeof(lapack_complex_float)); is not returning a pointer to an object of type lapack_complex_float.

Answer 2

I could compile it but you have to change the line
#include <lapacke.h>
to
#include <lapacke_utils.h>
You find at http://www.netlib.org/lapack/explore-html/da/d8e/lapacke__utils_8h_source.html. After you download it and put in the same directory of your program or use the tags -L -I to locate the library on your system during the compilation.
To compile use:
gcc CGEQRF_CUNGQR.c -llapacke -lblas -lm