User defined FFT function parameter not recognized

Hi All

I am trying to use the FFT function explained in this link

but when I use a nx2 signal and a scalar value for ScanRate I get an error :

Shall someone tell why isnt the function getting my input value

Unrecognized function or variable 'ScanRate'.

% function [frq, amp, phase] = simpleFFT( signal, ScanRate)
% Purpose: perform an FFT of a real-valued input signal, and generate the single-sided 

% output, in amplitude and phase, scaled to the same units as the input.

%inputs: 

%    signal: the signal to transform

%    ScanRate: the sampling frequency (in Hertz)

% outputs:

%    frq: a vector of frequency points (in Hertz)

%    amp: a vector of amplitudes (same units as the input signal)

%    phase: a vector of phases (in radians)

function [frq, amp, phase] = simpleFFT( signal, ScanRate)

n = length(signal); 

z = fft(signal, n); %do the actual work

%generate the vector of frequencies

halfn = floor(n / 2)+1;

deltaf = 1 / ( n / ScanRate);

frq = (0:(halfn-1)) * deltaf;

% convert from 2 sided spectrum to 1 sided

%(assuming that the input is a real signal)

amp(1) = abs(z(1)) ./ (n);

amp(2:(halfn-1)) = abs(z(2:(halfn-1))) ./ (n / 2); 

amp(halfn) = abs(z(halfn)) ./ (n); 

phase = angle(z(1:halfn));

[Image Analyst]

Show us how you instantiated the arguments that you passed in, and the line of code where you actually called the function with those variables.

You didn't just click the green Run triangle did you? Because that's a function where it won't run unless you pass in input arguments, which clicking the green run triangle won't do - it has no idea what you'd want for those variables.

[farzad]

it was a stupid wrong letter typo from me. sorry

when I do

plot( frq,amp)

the maximum value is not 1

applying on other signals with small values, around 1 to 4 mm , I get huge frf values of 180 mm or so

[farzad]

I think it has not mentioned how should be the time and amplitude be arranged in the signal matrix

Answer 1

[John D'Errico]

How did you call the function? When you get an error, report the ENTIRE error message, everyting in red. This lets us know how you called the function.

Just because you have a variable named ScanRate in your workspace does not tell MATLAB to automatically pass it into your function.

If you want the function to see the variable, then you NEED to pass it in. Call it like this:

[frq, amp, phase] = simpleFFT( signal, ScanRate);

So you need ot pass in TWO arguments to your function. They can have any names as you pass them in, but inside the function, now ScanRate will be defined.

If you don't, well, then MATLAB will generate an error - the one you got.

[farzad]

sure , here is the error

Unrecognized function or variable 'ScanRate'.

Error in 2020(line 6999)
                [frq, amp, phase] = simpleFFT(signal,ScanRate)
 
Error using matlab.ui.control.internal.controller.ComponentController/executeUserCallback (line 382)
Error while evaluating Button PrivateButtonPushedFcn.

[farzad]

ok it was a stupid wrong letter typo from me. sorry

now I tried the function, but I get a weird result from applying this FFT on my signal ,shall you try iy please

[farzad]

when I do

plot( frq,amp)

the maximum value is not 1

[farzad]

applying on other signals with small values, around 1 to 4 mm , I get huge frf values of 180 mm or so

[farzad]

I think it has not mentioned how should be the time and amplitude be arranged in the signal matrix