System of linear equations in fortran using DGESV [duplicate] - fortran

Question

I'm struggling with LAPACK's dgetrf and dgetri routines. Below is a subroutine I've created (the variable fit_coeffs is defined externally and is allocatable, it's not the problem). When I run I get memory allocation errors, that appear when I assign fit_coeffs, due to the matmul(ATA,AT) line. I know this from inserting a bunch of print statements. Also, both error checking statements after calls to LAPACK subroutines are printed, suggesting an error.
Does anyone understand where this comes from? I'm compiling using the command:
gfortran -Wall -cpp -std=f2003 -ffree-form -L/home/binningtont/lapack-3.4.0/ read_grib.f -llapack -lrefblas.
Thanks in advance!
subroutine polynomial_fit(x_array, y_array, D)
integer, intent(in) :: D
real, intent(in), dimension(:) :: x_array, y_array
real, allocatable, dimension(:,:) :: A, AT, ATA
real, allocatable, dimension(:) :: work
integer, dimension(:), allocatable :: pivot
integer :: l, m, n, lda, lwork, ok
l = D + 1
lda = l
lwork = l
allocate(fit_coeffs(l))
allocate(pivot(l))
allocate(work(l))
allocate(A(size(x_array),l))
allocate(AT(l,size(x_array)))
allocate(ATA(l,l))
do m = 1,size(x_array),1
do n = 1,l,1
A(m,n) = x_array(m)**(n-1)
end do
end do
AT = transpose(A)
ATA = matmul(AT,A)
call dgetrf(l, l, ATA, lda, pivot, ok)
! ATA is now represented as PLU (permutation, lower, upper)
if (ok /= 0) then
write(6,*) "HERE"
end if
call dgetri(l, ATA, lda, pivot, work, lwork, ok)
! ATA now contains the inverse of the matrix ATA
if (ok /= 0) then
write(6,*) "HERE"
end if
fit_coeffs = matmul(matmul(ATA,AT),y_array)
deallocate(pivot)
deallocate(fit_coeffs)
deallocate(work)
deallocate(A)
deallocate(AT)
deallocate(ATA)
end subroutine polynomial_fit

Answer 1

1) Where is fit_coeffs declared? I can't see how the above can even compile
1b) Implicit None is your friend!
2) You do have an interface in scope at the calling point, don't you?
3) dgertf and dgetri want "double precision" while you have single. So you need sgetrf and sgetri
"Fixing" all these and completeing the program I get
Program testit
Implicit None
Real, Dimension( 1:100 ) :: x, y
Integer :: D
Interface
subroutine polynomial_fit(x_array, y_array, D)
Implicit None ! Always use this!!
integer, intent(in) :: D
real, intent(in), dimension(:) :: x_array, y_array
End subroutine polynomial_fit
End Interface
Call Random_number( x )
Call Random_number( y )
D = 6
Call polynomial_fit( x, y, D )
End Program testit
subroutine polynomial_fit(x_array, y_array, D)
Implicit None ! Always use this!!
integer, intent(in) :: D
real, intent(in), dimension(:) :: x_array, y_array
real, allocatable, dimension(:,:) :: A, AT, ATA
real, allocatable, dimension(:) :: work, fit_coeffs
integer, dimension(:), allocatable :: pivot
integer :: l, m, n, lda, lwork, ok
l = D + 1
lda = l
lwork = l
allocate(fit_coeffs(l))
allocate(pivot(l))
allocate(work(l))
allocate(A(size(x_array),l))
allocate(AT(l,size(x_array)))
allocate(ATA(l,l))
do m = 1,size(x_array),1
do n = 1,l,1
A(m,n) = x_array(m)**(n-1)
end do
end do
AT = transpose(A)
ATA = matmul(AT,A)
call sgetrf(l, l, ATA, lda, pivot, ok)
! ATA is now represented as PLU (permutation, lower, upper)
if (ok /= 0) then
write(6,*) "HERE"
end if
call sgetri(l, ATA, lda, pivot, work, lwork, ok)
! ATA now contains the inverse of the matrix ATA
if (ok /= 0) then
write(6,*) "HERE"
end if
fit_coeffs = matmul(matmul(ATA,AT),y_array)
deallocate(pivot)
deallocate(fit_coeffs)
deallocate(work)
deallocate(A)
deallocate(AT)
deallocate(ATA)
end subroutine polynomial_fit
This runs to completion. If I omit the interface I get "HERE" printed twice. If I use the d versions I get seg faults.
Does this answer your question?