Warning: Integer operands are required for colon operator when used as index

I am using fft functions and have twice in my code this warning message, bu no clue why I get the warning:

N = 2048*16;
sizeData = size(data,2);
padding = (N-sizeData)/2;

cInput = zeros([1 N]); % <-- Warning
cInput(padding+1:(padding+sizeData)) = data;
cInput = fftshift(cInput);

% transform
cfourier = fftshift(fft(cInput));

% iFFt
cOutput = ifft(ifftshift(cfourier));
cOutput = ifftshift(cOutput); % <-- Warning
AmpIFourier = abs(cOutput(padding+1:(padding+sizeData)));

[Walter Roberson]

Haldun Hannis posted a question in the Answer section but deleted it while I was composing the reply. That reply follows:

(NFFT was constructed with 2^nextpow2 so is a power of 2)

WINDOW = hamming(NFFT/8+1);                                         % Windowing function
NOVERLAP=length(WINDOW)*0.5;

provided that the data is not very small, NFFT will be exactly divisible by 8 so NFFT/8 would be an even integer unless NFFT is 8 or less (not impossible, should be tested for.) With NFFT/8 being even, NFFT/8+1 will be odd. So you are asking for an odd-size hamming filter to be created.

You then take the length of that, which will be odd. And you multiply by 0.5. With it being odd, you will not get an integer result.

You then pass that non-integer value as the overlap size, into a function that uses it something vaguely like

data(start:start+overlap-1)

and that is a problem because overlap is not an integer

You should be using floor() or ceil() to force integer

Answer 1

[Image Analyst]

(N-sizeData)/2 can be a fractional number, e.g. "something point 5" so try

padding = floor((N-sizeData)/2);

or better yet, just use the padarray() function to do your padding.

[Jan]

While I agree, that this is correct, the OP told, that these lines produce the warnings:

cInput = zeros([1 N]); % <-- Warning

cOutput = ifftshift(cOutput); % <-- Warning

Isn't this strange?

[Image Analyst]

He didn't specify data. Just add this line before his code to generate his error:

data = rand(3)

but it actually comes at the line after the line he flagged, on line:

cInput(padding+1:(padding+sizeData)) = data;

he should have been more careful

[Matthias Pospiech]

The line number really are the ones that I marked. So do not blame me, blame matlab.

[Jan]

@Matthias: I've never seen a bug in Matlab, which leads to a wrong line number for warnings. While I assume IA and Oleg point to the correct solution, there must be an additional problem.

[Hannetjie]

@Jan Simon: It is now 3 years later so my apologies if this has since been touched upon in newer posts... But I came across this same anomaly (and this is the first and only time I've seen it). When running my code through, I get

Warning: Integer operands are required for colon operator when used as index > In tdnoise3 at 73

The warning in my case makes no sense at line nr 73. However, if I step through the exact same code, I get

Warning: Integer operands are required for colon operator when used as index > In tdnoise3 at 81

Which does make sense and was where the fix was required.

But OK, has no bearing on the topic of this post.

Answer 2

[Oleg Komarov]

Perfectly fine

idx = 2.5:9;

But when you use to index a position:

A = rand(10,1);
A(idx)

There's no such a thing as position number 2.5

Answer 3

[Jan]

N = 2048*16;
cInput = zeros([1 N]); % <-- Warning

No, I do not get a warning in this code. Are you sure, that this is the original code?