Combining python with fortran, tutorial problem
I am following this tutorial http://www.sam.math.ethz.ch/~raoulb/teaching/PythonTutorial/combining.html
I am using the same code
program hwtest
real*8 r1, r2 ,s
r1 = 1.0
r2 = 0.0
s = hw1(r1, r2)
write(*,*) 'hw1, result:',s
write(*,*) 'hw2, result:'
call hw2(r1, r2)
call hw3(r1, r2, s)
write(*,*) 'hw3, result:', s
end
real*8 function hw1(r1, r2)
real*8 r1, r2
hw1 = sin(r1 + r2)
return
end
subroutine hw2(r1, r2)
real*8 r1, r2, s
s = sin(r1 + r2)
write(*,1000) 'Hello, World! sin(',r1+r2,')=',s
1000 format(A,F6.3,A,F8.6)
return
end
C special version of hw1 where the result is
C returned as an argument:
subroutine hw3_v1(r1, r2, s)
real*8 r1, r2, s
s = sin(r1 + r2)
return
end
C F2py treats s as input arg. in hw3_v1; fix this:
subroutine hw3(r1, r2, s)
real*8 r1, r2, s
Cf2py intent(out) s
s = sin(r1 + r2)
return
end
C test case sensitivity:
subroutine Hw4(R1, R2, s)
real*8 R1, r2, S
Cf2py intent(out) s
s = SIN(r1 + r2)
ReTuRn
end
C end of F77 file
but when i use the command
f2py -m hw -c ../hw.f
I am getting the following error:
gfortran:f77: ../hw.f
../hw.f:5.13:
s = hw1(r1, r2)
1
Error: Return type mismatch of function 'hw1' at (1) (REAL(4)/REAL(8))
../hw.f:5.13:
s = hw1(r1, r2)
1
Error: Return type mismatch of function 'hw1' at (1) (REAL(4)/REAL(8))
error: Command "/usr/bin/gfortran -Wall -ffixed-form -fno-second-underscore -fPIC -O3 -funroll-loops -I/tmp/tmpRGHzqj/src.linux-x86_64-2.7 -I/usr/lib/python2.7/dist-packages/numpy/core/include -I/usr/include/python2.7 -c -c ../hw.f -o /tmp/tmpRGHzqj/fortran/hw.o" failed with exit status 1
I have no Fortran experience, I only need to implement existing Fortran code for use in Python.
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Your code is missing an interface for hw1
. Or specify it explicitly:
program hwtest
real*8 r1, r2 ,s
real*8 hw1
c [...]
Or better yet, put functions in a module and a use
module.
BTW: Change *8
to something more appropriate like:
program hwtest
integer,parameter :: dp = kind(1.d0)
real(dp) r1, r2 ,s
real(dp) hw1
Or use ISO_Fortran_env
both the predefined parameters REAL64
and REAL32
.
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Just to wrap things up:
program hwtest
implicit none
real*8 r1, r2 ,s
C Adding interface for the function
real*8 hw1
r1 = 1.0
r2 = 0.0
s = hw1(r1, r2)
write(*,*) 'hw1, result:',s
write(*,*) 'hw2, result:'
call hw2(r1, r2)
call hw3(r1, r2, s)
write(*,*) 'hw3, result:', s
end
real*8 function hw1(r1, r2)
real*8 r1, r2
hw1 = sin(r1 + r2)
return
end
subroutine hw2(r1, r2)
real*8 r1, r2, s
s = sin(r1 + r2)
write(*,1000) 'Hello, World! sin(',r1+r2,')=',s
1000 format(A,F6.3,A,F8.6)
return
end
C special version of hw1 where the result is
C returned as an argument:
subroutine hw3_v1(r1, r2, s)
real*8 r1, r2, s
s = sin(r1 + r2)
return
end
C F2py treats s as input arg. in hw3_v1; fix this:
subroutine hw3(r1, r2, s)
real*8 r1, r2, s
Cf2py intent(out) s
s = sin(r1 + r2)
return
end
C test case sensitivity:
subroutine Hw4(R1, R2, s)
real*8 R1, r2, S
Cf2py intent(out) s
s = SIN(r1 + r2)
ReTuRn
end
C end of F77 file
Compile with f2pyA -m hw -c hw.f
Finally, a call from python like:
import sys
from hw import hw1, hw2
try:
r1 = float(sys.argv[1]); r2 = float(sys.argv[2])
except IndexError:
print 'Usage:', sys.argv[0], 'r1 r2'; sys.exit(1)
print 'Fortran hw1, result:', hw1(r1, r2)
print 'Fortran hw2, result: ', hw2(r1, r2)
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