I need to implement a matrix class in C++ and one of the operations must be matrix multiplication via dgemm. My professor had done an example in class in C, but for some reason I can’t get it to work in C++. This is my header file matrix.h:
#include <iostream>
#include <stdlib.h>
extern "C" {
#include "blas.h"
}
[blah blah blah, matrix class here; overloaded * operator will do the matrix
multiplication]
matrix operator* (const matrix &other){
matrix AxB(Nrows, other.Ncolumns, "(" + name + "*" + "other.name" + ")");
char TRANSA = 'N';
char TRANSB = 'N';
int M = Nrows;
int N = other.Ncolumns;
int K = Ncolumns;
double alpha = 1.;
double beta = 0.;
dgemm_ (&TRANSA,
&TRANSB,
&M,
&N,
&K,
&alpha,
data,
&M,
other.data,
&K,
&beta,
AxB.data,
&M);
return AxB;
[blah blah blah, overloaded = operator here; i'm positive this is not the problem
since it works for matrix addition]
Main function:
#include "matrix.h"
main(){
// entries of A and B are randomized between 0 and 1
matrix A(5,5);
matrix B(5,5);
matrix C = A*B;
}
Now the blas.h header file:
void dgemm_ (char *TRANSA,
char *TRANSB,
int *M,
int *N,
int *K,
double *ALPHA,
double **A,
int *LDA,
double **B,
int *LDB,
double *BETA,
double **C,
int *LDC);
I’m to use the subroutine outlined here: http://www.netlib.org/blas/dgemm.f
Basically, the way we did it in class for the C implementation built a matrix as one long array using (double*) calloc(rows*columns, sizeof(double)).
My C++ implemenation does:
double **data;
data = new double[rows];
for(int i=1; i<=rows; ++i){
data[i-1] = new double[columns];
}
and then I can index using data[i][j]. But since the dgemm subroutine is supposed to take in double *A, double *B, etc. but my matrices are double **A and so on, how do I fix this?
This is the error message I get from valgrind:
==18845== Invalid write of size 8
==18845== at 0x4165C1C: ATL_dgezero (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4149DA7: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d680 is 8 bytes after a block of size 16 alloc'd
==18845== at 0x402B454: operator new[](unsigned int) (in /usr/lib/valgrind
/vgpreload_memcheck-x86-linux.so)
==18845== by 0x8049045: dmatrix::dmatrix(int, int, std::string) (dmatrix.hpp:77)
==18845== by 0x8049532: dmatrix::operator*(dmatrix const&) (dmatrix.hpp:218)
==18845== by 0x8048DCB: main (main.cpp:17)
==18845==
==18845== Invalid write of size 8
==18845== at 0x4165C1F: ATL_dgezero (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4149DA7: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d678 is 0 bytes after a block of size 16 alloc'd
==18845== at 0x402B454: operator new[](unsigned int) (in /usr/lib/valgrind
/vgpreload_memcheck-x86-linux.so)
==18845== by 0x8049045: dmatrix::dmatrix(int, int, std::string) (dmatrix.hpp:77)
==18845== by 0x8049532: dmatrix::operator*(dmatrix const&) (dmatrix.hpp:218)
==18845== by 0x8048DCB: main (main.cpp:17)
==18845==
==18845== Invalid write of size 8
==18845== at 0x4165C22: ATL_dgezero (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4149DA7: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d690 is not stack'd, malloc'd or (recently) free'd
==18845==
==18845== Invalid write of size 8
==18845== at 0x4165C25: ATL_dgezero (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4149DA7: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d688 is not stack'd, malloc'd or (recently) free'd
==18845==
==18845== Invalid read of size 8
==18845== at 0x4143D60: ATL_dJIK0x0x0NN0x0x0_aX_bX (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4149A9D: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478cf80 is not stack'd, malloc'd or (recently) free'd
==18845==
==18845== Invalid read of size 8
==18845== at 0x4143D64: ATL_dJIK0x0x0NN0x0x0_aX_bX (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4149A9D: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d130 is 0 bytes after a block of size 16 alloc'd
==18845== at 0x402B454: operator new[](unsigned int) (in /usr/lib/valgrind
/vgpreload_memcheck-x86-linux.so)
==18845== by 0x8049045: dmatrix::dmatrix(int, int, std::string) (dmatrix.hpp:77)
==18845== by 0x8048D49: main (main.cpp:6)
==18845==
==18845== Invalid read of size 8
==18845== at 0x4143D4C: ATL_dJIK0x0x0NN0x0x0_aX_bX (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4149A9D: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d678 is 0 bytes after a block of size 16 alloc'd
==18845== at 0x402B454: operator new[](unsigned int) (in /usr/lib/valgrind
/vgpreload_memcheck-x86-linux.so)
==18845== by 0x8049045: dmatrix::dmatrix(int, int, std::string) (dmatrix.hpp:77)
==18845== by 0x8049532: dmatrix::operator*(dmatrix const&) (dmatrix.hpp:218)
==18845== by 0x8048DCB: main (main.cpp:17)
==18845==
==18845== Invalid write of size 8
==18845== at 0x4143D93: ATL_dJIK0x0x0NN0x0x0_aX_bX (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4149A9D: ATL_dNCmmJIK (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x415BE8E: ATL_dgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x4182F54: ATL_dptgemm_nt (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4183140: ATL_dptgemm (in /usr/lib/atlas-base/atlas/libblas.so.3gf.0)
==18845== by 0x40818F6: atl_f77wrap_dgemm_ (in /usr/lib/atlas-base/atlas
/libblas.so.3gf.0)
==18845== by 0x4E4E0004: ???
==18845== Address 0x478d678 is 0 bytes after a block of size 16 alloc'd
==18845== at 0x402B454: operator new[](unsigned int) (in /usr/lib/valgrind
/vgpreload_memcheck-x86-linux.so)
==18845== by 0x8049045: dmatrix::dmatrix(int, int, std::string) (dmatrix.hpp:77)
==18845== by 0x8049532: dmatrix::operator*(dmatrix const&) (dmatrix.hpp:218)
==18845== by 0x8048DCB: main (main.cpp:17)
==18845==
==18845== Invalid read of size 8
==18845== at 0x8048DEA: main (main.cpp:19)
==18845== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==18845==
==18845==
==18845== Process terminating with default action of signal 11 (SIGSEGV)
==18845== Access not within mapped region at address 0x0
==18845== at 0x8048DEA: main (main.cpp:19)
==18845== If you believe this happened as a result of a stack
==18845== overflow in your program's main thread (unlikely but
==18845== possible), you can try to increase the size of the
==18845== main thread stack using the --main-stacksize= flag.
==18845== The main thread stack size used in this run was 8388608.
==18845==
==18845== HEAP SUMMARY:
==18845== in use at exit: 3,581 bytes in 39 blocks
==18845== total heap usage: 49 allocs, 10 frees, 7,760 bytes allocated
==18845==
==18845== LEAK SUMMARY:
==18845== definitely lost: 128 bytes in 4 blocks
==18845== indirectly lost: 0 bytes in 0 blocks
==18845== possibly lost: 88 bytes in 4 blocks
==18845== still reachable: 3,365 bytes in 31 blocks
==18845== suppressed: 0 bytes in 0 blocks
==18845== Rerun with --leak-check=full to see details of leaked memory
==18845==
==18845== For counts of detected and suppressed errors, rerun with: -v
==18845== ERROR SUMMARY: 111 errors from 9 contexts (suppressed: 0 from 0)
Segmentation fault (core dumped)
up until I try to implement the dgemm matrix multiplication, I get no errors and no leaks, so I’m pretty sure all my troubles lie with the dgemm implementation
The memory layout of the C version is different from the memory layout in your C++ version. As BLAS expects the kind of layout used by the C version, your C++ version won’t work.
Thus, you need to allocate a big 1-D array in your C++ version as well; you could overload operator() in order to get indexing for 2D arrays. Or for production code, use a library such as Eigen.