[Octave-bug-tracker] [bug #29601] bugs in cubic and spline interpolation with interp2

[Søren Hauberg]

Follow-up Comment #3, bug #29601 (project octave):

Sorry about the late reply (the last half year has been crazy for me...). To
be honest I am not sure if I am the author of the code in question (I might
be; I just don't remember), but I'll do a review anyway :-)

  - ## If X and Y vectors produce a grid from them
  + ## Check dimensions of X and Y
  if (isvector (X) && isvector (Y))
  X = X(:).';
  Y = Y(:);

Seems like a reasonable change to me (the new comment is more descriptive).

  - ## If Xi and Yi are vectors of different orientation build a grid
  - if ((rows (XI) == 1 && columns (YI) == 1)
  - || (columns (XI) == 1 && rows (YI) == 1))
  - ## Do nothing
  + ## Check dimensions of XI and YI
  + if (isvector (XI) && isvector (YI))
  + XI = XI(:).';
  + YI = YI(:);

This seems simpler then the current code. I am not sure if the

  + XI = XI(:).';
  + YI = YI(:);

part is really needed, but I guess it is better to play it safe, so this
seems fine to me.

  function b = isgriddata (X)
  d1 = diff (X, 1, 1);
  - d2 = diff (X, 1, 2);
  - b = all (d1 (:) == 0) & all (d2 (:) == d2 (1));
  + b = all (d1 (:) == 0);
  endfunction

This removes the check that the derivative of X is constant. I guess this is
not a requirement for X to be gridded (consider e.g. the output of 'meshgrid
(logspace (1, 10, 10))'). So, I think this change is fine as well.

In summary, I'd say check in the change.

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