Difference between revisions of "Fortran issues"
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import>Jss43 |
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1.234560 |
1.234560 |
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1.23456000000000 |
1.23456000000000 |
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| + | </pre> |
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| + | |||
| + | But the -r8 flag can help. It's safer to specify the kind in the code though. |
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| + | |||
| + | <pre> |
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| + | jss43@keiko:~/src/test> more testkind.f90 && ifort -r8 testkind.f90 && ./a.out program testkind |
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| + | implicit none |
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| + | integer,parameter :: r1=kind(0.0) |
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| + | integer,parameter :: r2=kind(0.d0) |
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| + | write (6,'(/a/)') 'Output:' |
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| + | write (6,*) real(1) |
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| + | write (6,*) real(1,r1) |
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| + | write (6,*) real(1,r2) |
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| + | write (6,*) real(1.23456d0) |
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| + | write (6,*) real(1.23456d0,r1) |
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| + | write (6,*) real(1.23456d0,r2) |
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| + | write (6,*) real(dcmplx(1.23456d0,0.2155660d0)) |
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| + | write (6,*) real(dcmplx(1.23456d0,0.2155660d0),r1) |
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| + | write (6,*) real(dcmplx(1.23456d0,0.2155660d0),r2) |
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| + | end program testkind |
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| + | |||
| + | Output: |
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| + | |||
| + | 1.00000000000000 |
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| + | 1.00000000000000 |
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| + | 1.00000000000000 |
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| + | 1.23456000000000 |
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| + | 1.23456000000000 |
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| + | 1.23456000000000 |
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| + | 1.23456000000000 |
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| + | 1.23456000000000 |
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| + | 1.23456000000000 |
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</pre> |
</pre> |
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Revision as of 15:54, 25 June 2008
I thought it would be useful to have a page for noting Fortran problems which aren't well documented elsewhere or are common gotchas... --james 16:23, 25 June 2008 (BST)
Real intrinsic
Care needs to be taken with using REAL(X). The default behaviour for REAL differs if X is complex rather than integer or real. Some googling reveals this is an oddity, but it is the specification. I have found that DREAL isn't always portable (some compilers have issues when the argument to DREAL is the value of a derived type, e.g. DREAL(X%v) fails at compile time but REAL(X%v) doesn't).
keiko:~/src/test> more testkind.f90 && ifort testkind.f90 && ./a.out
program testkind
implicit none
integer,parameter :: r1=kind(0.0)
integer,parameter :: r2=kind(0.d0)
write (6,'(/a/)') 'Output:'
write (6,*) real(1)
write (6,*) real(1,r1)
write (6,*) real(1,r2)
write (6,*) real(1.23456d0)
write (6,*) real(1.23456d0,r1)
write (6,*) real(1.23456d0,r2)
write (6,*) real(dcmplx(1.23456d0,0.2155660d0))
write (6,*) real(dcmplx(1.23456d0,0.2155660d0),r1)
write (6,*) real(dcmplx(1.23456d0,0.2155660d0),r2)
end program testkind
Output:
1.000000
1.000000
1.00000000000000
1.234560
1.234560
1.23456000000000
1.23456000000000
1.234560
1.23456000000000
But the -r8 flag can help. It's safer to specify the kind in the code though.
jss43@keiko:~/src/test> more testkind.f90 && ifort -r8 testkind.f90 && ./a.out program testkind
implicit none
integer,parameter :: r1=kind(0.0)
integer,parameter :: r2=kind(0.d0)
write (6,'(/a/)') 'Output:'
write (6,*) real(1)
write (6,*) real(1,r1)
write (6,*) real(1,r2)
write (6,*) real(1.23456d0)
write (6,*) real(1.23456d0,r1)
write (6,*) real(1.23456d0,r2)
write (6,*) real(dcmplx(1.23456d0,0.2155660d0))
write (6,*) real(dcmplx(1.23456d0,0.2155660d0),r1)
write (6,*) real(dcmplx(1.23456d0,0.2155660d0),r2)
end program testkind
Output:
1.00000000000000
1.00000000000000
1.00000000000000
1.23456000000000
1.23456000000000
1.23456000000000
1.23456000000000
1.23456000000000
1.23456000000000