MATLAB: Does the GRIDDATAN function return NaN values when interpolating data points that are generated from smooth functions

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For certain cases, when I use the GRIDDATAN function to fit scattered data, the function returns NaN values. The data points are generated from smooth functions and none are external to the data, therefore I do not expect to see any NaN values in the output.

The attached file contains code that can reproduce this error.

Best Answer

This bug has been fixed in Release 14 Service Pack 3 (R14SP3). For previous product releases, read below for any possible workarounds:

We have verified that there is a bug in MATLAB 7.0 (R14) that occurs when using the GRIDDATAN function.

There are currently no known workarounds.

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MATLAB: Does the INTERP1 function in MATLAB handle complex data with the “cubic” method

This enhancement has been incorporated in Release 2006a (R2006a). For previous product releases, read below for any possible workarounds:

The cubic interpolation algorithm is not intended for complex data and hence does not behave well under certain circumstances when the data is complex. As a workaround, use the spline interpolation instead.

Y_spline = interp1(X,Y,Xi,'spline');
plot(X,abs(Y),'b',Xi,abs(Y_spline),'r')

Alternatively, you can split Y into real and imaginary parts, and then interpolate.

Yr = real(Y);
Yi = imag(Y);
Y_cubic = interp1(X,Yr,Xi,'cubic')+i*interp1(X,Yi,Xi,'cubic');
plot(X,abs(Y),'b',Xi,abs(Y_cubic),'r')

MATLAB: TriScatteredInterp and ScatteredInterpolant functions produce different results

The 'TriScatteredInterp' function does not perform any extrapolation, whereas the 'scatteredInterpolant' function performs extrapolation by default.

Specifically, the 'scatteredInterpolant' function defaults to the extrapolation method of 'linear' when the interpolation method is 'linear' or 'natural' and the extrapolation method of 'nearest' when the interpolation method is 'nearest,' as described in the documentation found below under 'ExtrapolationMethod':

https://www.mathworks.com/help/matlab/ref/scatteredinterpolant.html

This can be resolved by manually setting the extrapolation method to 'none' in the call to 'scatteredInterpolant.' For example, the following lines of code should produce the same result for vectors x, y, and v:

>>scatteredInterpolant(x, y, v, 'linear', 'none')
>>TriScatteredInterp(x, y, v, 'linear')

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MATLAB: Does the INTERP1 function in MATLAB handle complex data with the “cubic” method

MATLAB: TriScatteredInterp and ScatteredInterpolant functions produce different results

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