# bug #38917: interp1 gives inconsistent results

 Submitted by: None Submitted on: Tue 07 May 2013 05:17:57 AM UTC Category: Libraries Severity: 3 - Normal Priority: 5 - Normal Item Group: Inaccurate Result Status: Fixed Assigned to: None Originator Name: Ted12201 Originator Email: -email is unavailable- Open/Closed: Closed Release: 3.6.4 Operating System: Any

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Wed 19 Jun 2013 07:13:56 PM UTC, comment #1:

Happily, this has already been fixed in the development code. To access the fix you will need to build from development sources or wait until the next major release of Octave (3.8).

Rik <rik5>
Tue 07 May 2013 05:17:57 AM UTC, original submission:

interp1(x,y,z) returns different results from MatLab and SciLab when both y and z are matrices. It appears that MatLab and SciLab results are correct.

For example,

x=1:30;
y=[x.^2; x.^0.5];
z=2:5;
X=X';
y=y';
z=z';
z=[z.^2 z.^0.5];
interp1(x,y,z)
interp1(x,y,z(:,1))
interp1(x,y,z(:,2))

Both Matlab and Scilab return

ans(:,:,1) =
16.0000 2.2426
81.0000 3.1962
256.0000 4.0000
625.0000 5.1803

ans(:,:,2) =
2.0000 1.1716
3.0000 1.3032
4.0000 1.4142
5.0000 1.4892

ans =
16 2
81 3
256 4
625 5

ans =
2.2426 1.1716
3.1962 1.3032
4.0000 1.4142
5.1803 1.4892

But Octave returns

ans(:,:,1) =
16.0000 2.2426
81.0000 1.0000
256.0000 6.0711
625.0000 4.0000

ans(:,:,2) =
2.0000 1.3032
3.0000 1.0978
4.0000 1.6469
5.0000 1.4892

ans =
16 2
81 3
256 4
625 5

ans =
2.2426 1.1716
3.1962 1.3032
4.0000 1.4142
5.1803 1.4892

These results suggest Octave is calculating correctly when a vector is given as z but not when it is a matrix.

Anonymous

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