[SciPy-user] doctest fortran I/O synchronization

[Todd Miller]

Hi Pearu,

Sorry about the example mismatch.  Your explanation of what to do with
the array loops will eventually be a big help.  Thanks!

Todd

On Fri, 2003-10-10 at 10:54, Pearu Peterson wrote:
> 
> Hi Todd,
> 
> On 10 Oct 2003, Todd Miller wrote:
> 
> > I'm trying to make a doctest to verify that the different flow patterns
> > of f2py interfaces work with different varieties of numarrays (normal,
> > byte-swapped, misaligned, dis-contiguous, type-converted).  I'm trying
> > to test this out under Linux with g77, and (it seems like) I'm having
> > trouble synchronizing the Fortran I/O with Python's C I/O.
> > 
> > Given foo.f:
> > 
> >       subroutine in_c(a,m,n)
> >       real*8 a(n,m)
> > Cf2py intent(in,c) a
> > Cf2py depend(a) ::  n=shape(a,0),  m=shape(a,1)
> >       do j=1,m
> >          do i=1,n
> >             write (6,1) a(i,j)
> >  1          format( $, 1F3.0, ', ')
> >          enddo
> >          print *,''
> >       enddo
> >       end
> > 
> > And given f2py_tests.py:
> 
> > """
> > >>> foo.in_f(a)
> <snip>
> 
> I could not run given tests as they were not complete and had typos.
> For instance, foo.f defines in_c but in test string you are using in_f.
> Also AFAIK, Python I/O will not catch I/O from Fortran.

This is good to know.  FWIW,  it seems Python I/O eventually catches
some of Fortran I/O, just not all of it.

> 
> Any way, when I modify in_c to in_f then the following code
> 
>   a = numarray.arange(15., shape=(3,5))
>   print a
>   foo.in_f(a)
> 
> outputs:
> 
> [[  0.   1.   2.   3.   4.]
>  [  5.   6.   7.   8.   9.]
>  [ 10.  11.  12.  13.  14.]]
>  0.,  1.,  2.,  
>  3.,  4.,  5.,  
>  6.,  7.,  8.,  
>  9., 10., 11.,  
> 12., 13., 14.,  
> 
> You probaly would not expect this. This is related to different storage 
> order in C and Fortran, of cource, and you have disabled f2py ability to 
> take into account this by using intent(c).
> 
> So, when you would not use intent(c), that is, in foo.f is a line
> 
>   Cf2py intent(in) a
> 
> then the following output occurs:
> 
> [[  0.   1.   2.   3.   4.]
>  [  5.   6.   7.   8.   9.]
>  [ 10.  11.  12.  13.  14.]]
>  0.,  5., 10.,  
>  1.,  6., 11.,  
>  2.,  7., 12.,  
>  3.,  8., 13.,  
>  4.,  9., 14.,  
> 
> The arrays look transposed because in Fortran your row index varies 
> faster, that is, a transposed array is displayed.
> 
> To sum up, don't use intent(c) and change the order of loops in in_f 
> function to get matching results.
> 
> HTH,
>   Pearu
> 
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-- 
Todd Miller 			jmiller at stsci.edu
STSCI / ESS / SSB