sgels function return different answers for mkl 18.5 and 19.5

gn164 — Tue, 27 Oct 2020 22:52:58 GMT

The following code that calls sgels returns different answers depending on whether I link with mkl 18.5 or 19.5. Also mkl 18.5 seems return different results depending on different machines.

My link command :

/opt/intel/19/bin/ifort reproduce.f90 -Wl,--start-group ${MKLROOT}/lib/intel64/libmkl_intel_lp64.a ${MKLROOT}/lib/intel64/libmkl_intel_thread.a ${MKLROOT}/lib/intel64/libmkl_core.a -Wl,--end-group -liomp5 -lpthread -lm -ldl -I${MKLROOT}/include

program reproduce implicit none integer :: row_A, col_A, row_B, col_B, info integer :: i real, allocatable :: A(:,:), B(:,:), work(:,:) ! allocate input matrices row_A = 2 col_A = 2 row_B = 2 col_B = 1 allocate(A(row_A,col_A)) allocate(B(row_B,col_B)) allocate(work(row_A*row_B,col_A*col_B)) A = 1 B = 1490.890 ! sgels call sgels('N', size(A,1), size(A,2), size(B,2), A, size(A,1), B, & size(B,1), work, size(work), info) ! check write(*,*) '--> A matrix' do i = 1, ubound(A, 1) write(*,*) A(i, :) end do write(*,*) '--> B matrix' do i = 1, ubound(B, 1) write(*,*) B(i, :) end do write(*,*) '--> Info' write(*,*) info deallocate(A, B, work) end program

Output for mkl 19 on skylake (Intel(R) Xeon(R) W-2145 CPU @ 3.70GHz)

--> A matrix
-1.414214 -1.414214
0.4142135 0.0000000E+00
--> B matrix
-2108.437
8.2589657E-05
--> Info

Output for mkl 18 on skylake (Intel(R) Xeon(R) W-2145 CPU @ 3.70GHz)

--> A matrix
-1.414214 -1.414214
0.4142135 1.9078982E-08
--> B matrix
-2837.939
4328.829
--> Info
0

Output for mkl 18 on sandybridge ( Intel(R) Xeon(R) CPU E5-2640 0 @ 2.50GHz)

--> A matrix
-1.414214 -1.414214
0.4142135 0.0000000E+00
--> B matrix
-2108.437
1.2207031E-04
--> Info
2

Re: sgels function return different answers for mkl 18.5 and 19.5

mecej4 — Wed, 28 Oct 2020 00:46:04 GMT

The MKL documentation for ?gels says, "It is assumed that A has full rank". Your matrix is of size 2 X 2 but its rank is only 1, so the input to the routine is improper. In such cases, what is the point of comparing the output, which could well be meaningless?

topic Re: sgels function return different answers for mkl 18.5 and 19.5 in Intel® oneAPI Math Kernel Library

sgels function return different answers for mkl 18.5 and 19.5

Re: sgels function return different answers for mkl 18.5 and 19.5