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Re: Interp2 cubic. Diff between Matlab and Octave


From: Ben Abbott
Subject: Re: Interp2 cubic. Diff between Matlab and Octave
Date: Sun, 10 May 2009 21:06:25 -0400


On May 10, 2009, at 5:55 PM, Andres Sepulveda wrote:

Hi,

We want to port a Matlab code to Octave but where it uses the interp2
function with the 'cubic'  flag we get the following diference. Any
idea why this happens?

Andres Sepulveda
University of Concepcion, CHILE

clear;
close all;
clc;

if exist('OCTAVE_VERSION')
        sufix = 'octave';
else
        sufix = 'matlab';
end

% original data --> {x,y,data}
[x,y] = meshgrid(1:11,1:3);
data = [0.41 0.40 0.73 0.77 0.48 0.11 0.74 0.06 0.57 0.83 0.46; ...
       0.98 0.32 0.54 0.38 0.19 0.30 0.33 0.03 0.68 0.07 0.44; ...
       0.69 0.98 0.16 0.95 0.67 0.25 0.35 0.50 0.40 0.46 0.63];

% interpolated data --> {lon,lat,rr_}
lon = linspace(x(1),x(end),25);
lat = linspace(y(1),y(end),25);
rr1 = interp2(x,y,data,lon,lat,'linear'); % linear
rr2 = interp2(x,y,data,lon,lat,'cubic');  % cubic

% plot result
figure;
plot(rr1,'linewidth',2);
axis([1 25 0 1]);
title(['linear interpolation ',sufix]);
print(['linear_',sufix,'.eps'],'-depsc');

figure;
plot(rr2,'linewidth',2);
axis([1 25 0 1]);
title(['cubic interpolation ',sufix]);
print(['cubic_',sufix,'.eps'],'-depsc');

Using Matlab, both results look quite similar.

It appears to me that the cubic interpolation is not working correctly.

Jaroslav, can you confirm?

Ben




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