CSR space matrix vector product with stdlib

[tof92130]

Description

Hello,

1/ With gnu compilers, I am using subroutine spmv from stdlib in order to realize a CSR sparse matrix vector product :

call spmv(matrix=mat%STDL, vec_x=x0, vec_y=x1, alpha=alpha, beta=beta) !> x1 = alpha mat%STDL x0 + beta x0

2/ With Intel compilers, I am using mkl_dcsrmv subroutine for same operation.

3/ I also have a my own procedure for this operation.

If beta=0 we should find x1 = mat%STDL x0

it I the case with mkl_dcsrmv and my own procedure but to obtain this result with procedure spmv from sodlib I must initialize x1(:) to 0d0 before (not good for bandwidth).

Here is my own procedure:

          do iRow=1,size(mat%STDL%rowptr)-1
            x1(iRow)=beta*x1(iRow)
            !$OMP SIMD
            do jMat=mat%STDL%rowptr(iRow),mat%STDL%rowptr(iRow+1)-1
              x1(iRow)=x1(iRow)+alpha*mat%STDL%data(jMat)*x0(mat%STDL%col(jMat))
            enddo
          enddo

line 2 initialise x1 to zero if beta=0.

Expected Behaviour

initialize x1 to zero when beta=0

Version of stdlib

60d0a76

Platform and Architecture

Mac/OS ARM and Intel

Additional Information

No response

[jalvesz]

Hi @tof92130, thanks for signaling this. I'm intrigued though:

At the beginning of the procedure one can find

stdlib/src/stdlib_sparse_spmv.fypp

Lines 148 to 152 in 60d0a76

	if(present(beta)) then
	vec_y = beta * vec_y
	else
	vec_y = zero_${s1}$
	endif

Which should clean y following:
y = alpha*op(matrix)*x + beta * y
y should indeed be zero if beta == 0. Could you show us the results you are obtaining?

[tof92130]

Indeed, it should work...

I investigate my program to see if the problem couldn't come from elsewhere (?)

[tof92130]

can you please close this issue.

I solved the problem by initialising x1(:) and x2(:) just after first initialisation. Size of x1(:) and x2(:) are larger than size(mat%STDL%rowptr)-1 because I also include place for MPI exchange and I probably introduced bad values because of that.

intel compilers initialize to zero after allocation, gnu compilers do not.