From bug-request at octave dot org Thu Jan  5 05:53:42 2006
Subject: interp1.m (octave-forge) *linear
From: Olaf Till <olaf dot till at uni-jena dot de>
To: bug at octave dot org
Date: Thu, 5 Jan 2006 03:04:39 -0600

This is a bug in a component of octave-forge, please forward if this
is not the correct mailing list. If someone wants to respond --- I am
not subscribed to bug at octave dot org dot 

Function: interp1.m
Author: Paul Kienzle
Version: Date of last change documented in the file: 2002-01-23

Description:
In method '*linear' the results are different from method 'linear'
(despite of even spacing of x) when the difference between neighboured
x's is not equal to 1.

Suggested fix:

in lines 131 to 139:

  elseif strcmp(method, '*linear')
    ## find the interval containing the test point
    t = (xi - minx)/dx + 1;
    idx = floor(t);

    ## use the endpoints of the interval to define a line
    dy = [y(2:ny,:) - y(1:ny-1,:); zeros(1,nc)];
    s = (t - idx)./dx;
    yi(range,:) = s(:,ones(1,nc)).*dy(idx,:) + y(idx,:); 

there is a doubled division by `dx' (in line 133 and in line 138).
Changing line 138

    s = (t - idx)./dx;

to

    s = t - idx;

makes method '*linear' return the same results as 'linear' even with
non integer x's for me.

Regards, Olaf



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