Index exceeds matrix dimensions error

hi i was running this simple code,but i got this error,any idea how to fix it?

L = 140;                     % Length of signal         
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
YY = fft(rawdata,NFFT)/L;

((((((((((Index exceeds matrix dimensions.))))))))

Error in Untitled2 (line 11)
YY = fft(rawdata,NFFT)/L;

[Image Analyst]

Before the YY line, put this and tell us what it says

whos rawdata
NFFT

Is NFFT > the dimensions of rawdata?

[mohamad mohamad]

thanks for your fast reply, i did what you said,here are the result

Name           Size            Bytes  Class     Attributes

rawdata      140x1              1120  double

NFFT =

   256

[Star Strider]

Next step:

In the Command Window, type

which fft -all

after the error.

I get 6 answers, all in: C:\Program Files\MATLAB\.

[mohamad mohamad]

fft is a variable.
built-in (C:\MATLAB\R2012a\toolbox\matlab\datafun\@logical\fft)  % Shadowed logical method
built-in (C:\MATLAB\R2012a\toolbox\matlab\datafun\@single\fft)   % Shadowed single method
built-in (C:\MATLAB\R2012a\toolbox\matlab\datafun\@double\fft)   % Shadowed double method
C:\MATLAB\R2012a\toolbox\matlab\datafun\@uint8\fft.m             % Shadowed uint8 method
C:\MATLAB\R2012a\toolbox\matlab\datafun\@uint16\fft.m            % Shadowed uint16 method
C:\MATLAB\R2012a\toolbox\comm\comm\@gf\fft.m                     % Shadowed gf method
C:\MATLAB\R2012a\toolbox\distcomp\parallel\@codistributed\fft.m  % Shadowed codistributed method
C:\MATLAB\R2012a\toolbox\dsp\filterdesign\@qfft\fft.m            % Shadowed qfft method
C:\MATLAB\R2012a\toolbox\ident\ident\@iddata\fft.m               % Shadowed iddata method

Answer 1

[Image Analyst]

How can you take 256 samples from an array with 140 samples? Maybe you need to pad it with zeros or something

newArray = [oldArray, zeros(1, NFFT - length(oldArray))];

[Image Analyst]

Actually it says it does the padding for you so you should be okay: "Y = fft(X,n) returns the n-point DFT. fft(X) is equivalent to fft(X, n) where n is the size of X in the first nonsingleton dimension. If the length of X is less than n, X is padded with trailing zeros to length n. "

Try Star's suggestion of

which -all fft

And see if it says this:

built-in (C:\Program Files\MATLAB\R2014b\toolbox\matlab\datafun\@logical\fft)  % logical method
built-in (C:\Program Files\MATLAB\R2014b\toolbox\matlab\datafun\@single\fft)   % single method
built-in (C:\Program Files\MATLAB\R2014b\toolbox\matlab\datafun\@double\fft)   % double method
C:\Program Files\MATLAB\R2014b\toolbox\matlab\datafun\@uint8\fft.m             % uint8 method
C:\Program Files\MATLAB\R2014b\toolbox\matlab\datafun\@uint16\fft.m            % uint16 method

or does it have some folders with your name in them?

[mohamad mohamad]

thanks for your replay i did what u said,and pad it with zeros but i got this new error

Error using horzcat CAT arguments dimensions are not consistent.

Error in Untitled2 (line 11) newArray = [rawdata, zeros(1, NFFT - length(rawdata))];

[mohamad mohamad]

i tried 'which -all fft' i had all the files that you mentioned

[Image Analyst]

Like Star said, you have a variable called fft, apparently in some code you didn't show us. Rename that variable.

[mohamad mohamad]

my vector was a column vector and could not be concatenated with row vector zeros(1, NFFT - length(rawdata)).so i changed it to zeros(NFFT - (length(rawdata)), 1)]; and it works properly thanks indeed for your fast replays

[Image Analyst]

OK, glad it works, though I don't know why since the help for fft() said that it would do that padding for you.