Does the INTERP1 function in MATLAB handle complex data with the "cubic" method?

I have "X" and "Y" data. "Y" is complex. I use the INTERP1 function with cubic interpolation to interpolate the data as follows:

Y_cubic = interp1(X,Y,Xi,'cubic');

plot(X,abs(Y),'b',Xi,abs(Y_cubic),'r')

In the resulting plot, I find there are some sharp peaks that do not seem correct.

Answer 1

[MathWorks Support Team]

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')