Explanation for : Warning: Integer operands are required for colon operator when used as index. > In welch>loca​lComputeSp​ectra (line 379)

Hi

I am getting the following warning when I use mscohere() and tfestimate()

Warning: Integer operands are required for colon operator when used as index. 
> In welch>localComputeSpectra (line 379)
In welch (line 170)
In tfestimate (line 151)
In BandwidthPhaseDelayCalculator (line 50)
In WingBorneFlightPathChirpsForPitchRateLOES_MatlabWrapper (line 131)
In WingBorneLOESDataExtractorLocalOnly (line 116)

The warning comes on for the following commands :

[CF,frq1] = mscohere(u, y, wind, No, NFFT, 1/dti);

and

[TF,frq2] = tfestimate(u, y, wind, No, NFFT, 1/dti);

I believe this error is due to the windowing and other parameters being sent to the functions, If I just use the u, y input arguments for arrays into both functions, I don't get this warning.

I want to understand the following:

1. Why I am getting this warning?
2. What does this warning actually mean?
3. How is MATLAB handling this error with non integer operands.

Answer 1

[Walter Roberson]

Your No variable corresponds to the overlap which is required to be a positive integer according to the documentation. However whatever you are passing in there is not an integer.

The internal code is doing

LminusOverlap = L-noverlap;
xStart = 1:LminusOverlap:k*LminusOverlap;
xEnd   = xStart+L-1;

If your supplied an overlap that is not an integer, then LminusOverlap will not be an integer, and the 1:LminusOverlap:k*LminusOverlap will generate a sequence of values that are not all integers.

The code then later has

         [Sxxk,w] =  computeperiodogram({x(xStart(ii):xEnd(ii),:),...
             y(xStart(ii):xEnd(ii),:)},win,options.nfft,esttype,options.Fs);

so it tries to use the computed xStart values as indices into x but you have a problem using those values as indices when one of them is not an integer.

You can only overlap by a whole number of samples, not by a fraction of a sample.