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Re: How does Math::GSL accept data?

by Anonymous Monk
on May 18, 2009 at 16:35 UTC ( [id://764668]=note: print w/replies, xml ) Need Help??


in reply to How does Math::GSL accept data?

http://cpansearch.perl.org/src/LETO/Math-GSL-0.18/t/Histogram.t
$stream = gsl_fopen("histogram", 'r'); my $h = gsl_histogram_alloc(100); ok_status(gsl_histogram_fread($stream, $h));
so
my $fi = gsl_fopen( 'infile','r');

Replies are listed 'Best First'.
Re^2: How does Math::GSL accept data?
by hda (Chaplain) on May 21, 2009 at 17:22 UTC
    Hi! thanks for your answer, but unfortunately I cannot make it to work. Here is the beggining of my data:

    1 3 25 1 5 1 3 1 2 2 3 3 3 25 1 1 5 2 4500 1 1 1 1 5 5 8000 1 1 5 500 1 1 1 5 2 1 1 1000 1000 1000 1000 5000 1 25 6000 500 25 25 9000 1 1 5 1000 6000 25 10 5 5 5 5 1000 9540 1000 5 1 5 500 2500 2 5 5 5 ...

    Is just a sequence of integers, stored in a plain text file called "data".

    Now, this is my code:

    my $fi = gsl_fopen('data', 'r'); my $fo = gsl_fopen('hist', 'w'); my $h = gsl_histogram_alloc(6); my $range = [ 1.0, 10.0, 100.0, 1000.0, 10000.0, 100000.0 ]; gsl_histogram_fread($fi, $h); gsl_histogram_set_ranges($h,$range,7); gsl_histogram_fprintf($fo, $h, "%3.1f", "%3.1f"); gsl_fclose($fo); gsl_fclose($fi);

    What I need is to produce a histogram with 6 logarithmic bins (see the $range variable in the code). When I run this code I get no errors, and the result is:

    1.0 10.0 0.0
    10.0 100.0 0.0
    100.0 1000.0 0.0
    1000.0 10000.0 0.0
    10000.0 100000.0 0.0
    100000.0 0.0 0.0


    So, either no data is read or something of what I have no idea is going on. In the documentation one finds:

    gsl_histogram_fread($stream, $h) - This function reads into the histogram $h from the open stream $stream, which has been opened by the gsl_fopen function from the Math::GSL module, in binary format. The histogram $h must be preallocated with the correct size since the function uses the number of bins in $h to determine how many bytes to read. The return value is 0 for success and $GSL_EFAILED if there was a problem reading from the file. The data is assumed to have been written in the native binary format on the same architecture.

    But I find it a bit complicated to understand if a text file can be read or not. Oh wise monks! any hint will be appreciated!
      Well, I don't know Perl, but I do know GSL. Statemens in your code are in a wrong order. 1) Allocate 6 bins gsl_histogram* h=gsl_histogram_alloc(6); 2) Set the ranges. 6 bins require 7 points. (you have 6) double ranges7={1.,2.,3.,4.,5.,6.,7.}; gsl_histogram_set_ranges(h,ranges,7); 3) And only after initialization one can use the histogram 4) In C one should free the histogram after using it. No idea about Perl.

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