Index exceeds matrix dimensions error

2014 12 10
1 个回答
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更新时间：2014 12 10
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0 个投票

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;

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Image Analyst
Image Analyst 2014-12-10
Before the YY line, put this and tell us what it says
whos rawdata
NFFT
Is NFFT > the dimensions of rawdata?
mohamad mohamad
mohamad mohamad 2014-12-10
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
Star Strider 2014-12-10
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
mohamad mohamad 2014-12-10
编辑：Star Strider 2014-12-10
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

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 采纳的回答

Image Analyst
Image Analyst 2014-12-10

0 个投票

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))];

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Image Analyst
Image Analyst 2014-12-10
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
mohamad mohamad 2014-12-10
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
mohamad mohamad 2014-12-10
i tried 'which -all fft' i had all the files that you mentioned
Image Analyst
Image Analyst 2014-12-10
Like Star said, you have a variable called fft, apparently in some code you didn't show us. Rename that variable.
mohamad mohamad
mohamad mohamad 2014-12-10
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
Image Analyst 2014-12-10
OK, glad it works, though I don't know why since the help for fft() said that it would do that padding for you.

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