[Numpy-discussion] f2py and Fortran90 gfortran_filename error

Tyler Hayes hayes.tyler@gmail....
Wed Feb 28 08:16:27 CST 2007

```Hello All:

I was suggested to post this question here with the f2py experts from
comp.lang.python.

I have been able to use the example F77 files suggested in the f2py
User Manual, but the problems happened when I tried my own F90 file
(attached below.

I am able to create a <module_name>.so file using the following method:

(1) Created a Fortran90 program matsolve.f90

Note: The program compiles fine and prints the proper output for the
simple matrix specified.

(2) f2py matsolve.f90 -m matsolve2 -h matsolve2.pyf

This created the matsolve2.pyf fine

(3) f2py -c matsolve2.pyf --f90exec=/usr/bin/gfortran matsolve.f90

Note: I had to specify the f90exec path as f2py did not automatically find
it. This was the only way I could generate a *.so file.

The rub:

When I import it into Python, I receive the following
message:

>>> import matsolve2

Traceback (most recent call last):
File "<stdin>", line 1, in ?
ImportError: ./matsolve2.so: undefined symbol: _gfortran_filename

Any suggestions are greatly appreciated. (I almost started smoking
again last night! ARGH!)

Cheers,

t.

PS - Below I have attached the F90 program for LU decomposition with a
simple test case.

! MATSOLVE.f90
!
! Start main program
PROGRAM MATSOLVE
IMPLICIT NONE
INTEGER,PARAMETER :: n=3
INTEGER :: i,j
REAL,DIMENSION(n) :: x,b
REAL,DIMENSION(n,n) :: A,L,U
! Initialize the vectors and matrices with a test case from text
! Using the one given in Appendix A from Thompson.
! Known vector "b"
b(1) = 12.
b(2) = 11.
b(3) =  2.

! Known coefficient matrix "A", and initialize L and U
DO i=1,n
DO j=1,n
L(i,j) = 0.
U(i,j) = 0.
END DO
END DO

! Create matrix A
A(1,1) =  3.
A(1,2) = -1.
A(1,3) =  2.

A(2,1) = 1.
A(2,2) = 2.
A(2,3) = 3.

A(3,1) =  2.
A(3,2) = -2.
A(3,3) = -1.

! Call subroutine to create L and U matrices from A
CALL lumake(L,U,A,n)
! Print results
PRINT *, '-----------------------'
DO i=1,n
DO j=1,n
PRINT *, i, j, A(i,j), L(i,j), U(i,j)
END DO
END DO
PRINT *, '-----------------------'

! Call subroutine to solve for "x" using L and U
CALL lusolve(x,L,U,b,n)
! Print results
PRINT *, '-----------------------'
DO i=1,n
PRINT *, i, x(i)
END DO
PRINT *, '-----------------------'

END PROGRAM MATSOLVE

! Create subroutine to make L and U matrices
SUBROUTINE lumake(LL,UU,AA,n1)
IMPLICIT NONE
INTEGER,PARAMETER :: n=3
INTEGER :: i,j,k
REAL :: LUSUM
INTEGER,INTENT(IN) :: n1
REAL,DIMENSION(n,n),INTENT(IN) :: AA
REAL,DIMENSION(n,n),INTENT(OUT) :: LL,UU

! We first note that the diagonal in our UPPER matrix is
! going to be UU(j,j) = 1.0, this allows us to initialize
! the first set of expressions
UU(1,1) = 1.

! Find first column of LL
DO i = 1,n1
LL(i,1) = AA(i,1)/UU(1,1)
END DO

! Now find first row of UU
DO j = 2,n1
UU(1,j) = AA(1,j)/LL(1,1)
END DO

! Now find middle LL elements
DO j = 2,n1
DO i = j,n1
LUSUM = 0.
DO k = 1,j-1
LUSUM = LUSUM + LL(i,k)*UU(k,j)
END DO
LL(i,j) = AA(i,j) - LUSUM
END DO

! Set Diagonal UU
UU(j,j) = 1.

! Now find middle UU elements
DO i = j+1,n1
LUSUM = 0.
DO k = 1,j-1
LUSUM = LUSUM + LL(j,k)*UU(k,i)
END DO
UU(j,i) = (AA(j,i) - LUSUM)/LL(j,j)
END DO
END DO
END SUBROUTINE lumake

! Make subroutine to solve for x
SUBROUTINE lusolve(xx,L2,U2,bb,n2)
IMPLICIT NONE
INTEGER,PARAMETER :: n=3
INTEGER :: i,j,k
REAL :: LYSUM,UXSUM
REAL,DIMENSION(n):: y
INTEGER,INTENT(IN) :: n2
REAL,DIMENSION(n),INTENT(IN) :: bb
REAL,DIMENSION(n,n),INTENT(IN) :: L2,U2
REAL,DIMENSION(n),INTENT(OUT) :: xx

! Initialize
DO i=1,n2
y(i)  = 0.
xx(i) = 0.
END DO

! Solve L.y = b
y(1) = bb(1)/L2(1,1)
DO i = 2,n2
LYSUM = 0.
DO k = 1,i-1
LYSUM = LYSUM + L2(i,k)*y(k)
END DO
y(i) = (bb(i) - LYSUM)/L2(i,i)
END DO

! Now do back subsitution for U.x = y
xx(n2) = y(n2)/U2(n2,n2)
DO j = n2-1,1,-1
UXSUM = 0.
DO k = j+1,n2
UXSUM = UXSUM + U2(j,k)*xx(k)
END DO
xx(j) = y(j) - UXSUM
END DO
END SUBROUTINE lusolve

--
Tyler Joseph Hayes
600 Talbot St. -- Apt. 812
London, Ontario
N6A 5L9

Tel   : 519.435.0967
Fax  : 519.661.3198
Cell  : 416.655.7897
email: thayes@uwo.ca

GPG Key ID# 0x3AE05130
```