Package: ruby-lapack Version: 1.8.1-1 Severity: serious Tags: sid bookworm X-Debbugs-CC: debian...@lists.debian.org User: debian...@lists.debian.org Usertags: needs-update
Dear Maintainer, Since the upload of lapack 3.10.0-1, the autopkgtest of ruby-lapack fails in unstable. See for example: https://ci.debian.net/data/autopkgtest/unstable/amd64/r/ruby-lapack/15155031/log.gz More precisely, the tests about generalized singular value decomposition (GSVD) fail. Mathematically, the GSVD does not have a unique solution. For some reason, lapack 3.10 now returns a different (still valid) solution, but the ruby-lapack testsuite hardcodes another, specific, solution. Please find attached a Fortran 2008 source code through which I verified that the decomposition given by both lapack 3.9 and 3.10 is valid, though the Q matrix is different between the two versions. The code needs to be compiled with gfortran, and linked against -llapack. I verified only the double float decomposition (dggsvd), but the single float decomposition test (sggsvd) most likely fails for the same reason. The testsuite of ruby-lapack thus needs to be adapted, by allowing alternative solutions (either accept both the old and the new solutions, or completely rethink the test by only verifying the the decomposition is valid as I did in my program). N.B. : when trying to reproduce the problem, please ensure that your lapack alternative (as given by “update-alternatives --display liblapack.so.3-x86_64-linux-gnu) points to /usr/lib/x86_64-linux- gnu/lapack/liblapack.so.3, and not to the binary provided by either openblas or atlas (because these two have not yet been recompiled against lapack 3.10, and thus do not expose the problem). Best regards, -- ⢀⣴⠾⠻⢶⣦⠀ Sébastien Villemot ⣾⠁⢠⠒⠀⣿⡁ Debian Developer ⢿⡄⠘⠷⠚⠋⠀ https://sebastien.villemot.name ⠈⠳⣄⠀⠀⠀⠀ https://www.debian.org
program ggsvd
use iso_fortran_env
implicit none
interface
subroutine dggsvd(jobu, jobv, jobq, m, n, p, k, l, a, lda, b, &
ldb, alpha, beta, u, ldu, v, ldv, q, ldq, work, &
iwork, info)
import :: real64
real(real64), dimension(*), intent(inout) :: a, b
real(real64), dimension(*), intent(out) :: alpha, beta, q, u, v, work
character, intent(in) :: jobq, jobu, jobv
integer, intent(in) :: lda, ldb, ldq, ldu, ldv, m, n, p
integer, intent(out) :: info, k, l
integer, dimension(*), intent(out) :: iwork
end subroutine dggsvd
end interface
real(real64) :: a(4,3), b(2,3), alpha(3), beta(3), u(4,4), v(2,2), q(3,3),
work(12), d1(4,3), d2(2,3), a_bak(4,3), b_bak(2,3)
integer :: info, k, l, iwork(3)
a = reshape(source = [ real(real64) :: 1., 3., 4., 7., 2., 2., 5., 8., 3.,
1., 6., 8. ], shape = [4,3])
b = reshape(source = [ real(real64) :: -2., 4., -3., 6., 3., 5. ], shape = [
2, 3 ])
print '("A=",/,4(3es12.4,:,/))', transpose(a)
print '("B=",/,2(3es12.4,:,/))', transpose(b)
a_bak = a
b_bak = b
call dggsvd("U", "V", "Q", 4, 3, 2, k, l, a, 4, b, 2, alpha, beta, u, 4, v,
2, q, 3, work, iwork, info)
print '("U=",/,4(4es12.4,:,/))', transpose(u)
print '("V=",/,2(2es12.4,:,/))', transpose(v)
print '("Q=",/,3(3es12.4,:,/))', transpose(q)
print '("k=",i1)', k
print '("l=",i1)', l
if (k /= 1) stop "k is incorrect"
if (l /= 2) stop "l is incorrect"
! We are in the case where M-K-L>0
! Also note that N-K-L=0
d1 = 0._real64
d1(1,1) = 1._real64
d1(2,2) = alpha(2)
d1(3,3) = alpha(3)
d2 = 0._real64
d2(1,2) = beta(2)
d2(2,3) = beta(3)
associate (r => a(1:3,1:3))
associate (a2 => matmul(u, matmul(d1, matmul(r, transpose(q)))), &
b2 => matmul(v, matmul(d2, matmul(r, transpose(q)))))
print '("Error on reconstructed A: ", es12.4)', maxval(abs(a_bak-a2))
print '("Error on reconstructed B: ", es12.4)', maxval(abs(b_bak-b2))
end associate
end associate
end program ggsvd
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