Bug in xGEQRF Julia wrapper for matrices with zero columns #882
Description
The following linear algebra wrapper fails on matrices with zero number of columns:
LinearAlgebra.LAPACK.geqrf!(rand(2,0),zeros(0))
** On entry to DGEQRF parameter number 7 had an illegal value
ERROR: ArgumentError: invalid argument JuliaLang/julia#7 to LAPACK call
Stacktrace:
[1] chklapackerror(ret::Int64)
@ LinearAlgebra.LAPACK C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\LinearAlgebra\src\lapack.jl:36
[2] geqrf!(A::Matrix{Float64}, tau::Vector{Float64})
@ LinearAlgebra.LAPACK C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\LinearAlgebra\src\lapack.jl:519
[3] top-level scope
@ REPL[89]:1
The 7-th argument of the LAPACK subroutine DGEQRF is LWORK (the length of work array WORK) and it must satisfy LWORK >= max( 1, N ), where N is the column dimension of the matrix (in our case N = 0). In the Julia function geqrf!, a first call is performed with LWORK = -1, which is used to determine the optimal length of the work array, which is returned in WORK(1). I suspect that the returned value is 0 and therefore, at the second call LWORK = 0 is used, which leads to the above error. This error can be easily fixed in Julia, by replacing in geqrf!
lwork = BlasInt(real(work[1]))
by
lwork = max(1,BlasInt(real(work[1])))
at the second call.
Similar fix is necessary also for gerqf!, because
LinearAlgebra.LAPACK.gerqf!(rand(2,0),zeros(0))
** On entry to DGERQF parameter number 7 had an illegal value
ERROR: ArgumentError: invalid argument JuliaLang/julia#7 to LAPACK call
Stacktrace:
[1] chklapackerror(ret::Int64)
@ LinearAlgebra.LAPACK C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\LinearAlgebra\src\lapack.jl:36
[2] gerqf!(A::Matrix{Float64}, tau::Vector{Float64})
@ LinearAlgebra.LAPACK C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\LinearAlgebra\src\lapack.jl:548
[3] top-level scope
@ REPL[91]:1