Dynamic memory allocation error in Fortran2003 using LAPACK

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 al

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.

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