quote:

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It's possible that fft.nextPowerOf2 remains set by the total dataset size so you might try something like this...

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[fft]

//------------------------------------------------------------------------------
// FFT COMPUTATION
//------------------------------------------------------------------------------

%Z=%[%C,'_']; 		// name of wks containing Active dataset %C 
%A=%Z_%(%Z, @Xn); 	// name of X dataset (wks_dataset)
%B=%C;			// name of Y dataset (wks_daset)

ty [-----] F F T [-----];	// debug info
ty [Times dataset = %A];	// debug info
ty [Values dataset= %B];	// debug info

if ((mks1!=-1)&&(mks2!=-1))
{
	start=mks1;					// start from selection
	delta=mks2-mks1; 				// selection range dimension
	type Performing FFT between $(mks1) and $(mks2);// debug info
} 
else
{
	start=1;					// start from first row
	delta=%Z!wks.nrows;				// process all rows
	type Performing FFT over the whole data;	// debug info
}

fft.reset( );					// Reset previous fft settings
fft.start=1;	// These poperties doesn't work for fft object but i set them anyway
fft.size=delta;	// These poperties doesn't work for fft object but i set them anyway

zpt=1;				// next power of 2 after selected range rows amount
for(i=1;i>0;i++){zpt*=2; if(zpt>delta) break};
fft.nextPowerOf2=zpt; 		// set the proper power of 2 accoring to fft.size
type next power of 2 is $(zpt); // debug info

create tmp -wd delta Time Value;		// create a temporary worksheet --> Replace -wd with -w for debug <--
copy -b start %A tmp_Time -b 1 -e delta;  	// copy X dataset
copy -b start %B tmp_Value -b 1 -e delta; 	// copy Y dataset

fft.forward=1; 					// 1= forward 0=backward
fft.forward.timeData$=tmp_Time;			// Time values dataset
fft.forward.tdelta=tmp_Time[2]-tmp_Time[1];	// Sampling interval
fft.forward.realData$=tmp_Value;		// Values dataset
fft.forward.imagData$="";			// Set imaginary to Null

window -t W fft %ZFFT;	// Output worksheet

fft.output.samplingdata$=%ZFFT_Freq;
fft.output.realdata$=%ZFFT_Real;
fft.output.imagdata$=%ZFFT_Imag;
fft.output.ampdata$=%ZFFT_r;
fft.output.phasedata$=%ZFFT_Phi;
fft.output.powerdata$=%ZFFT_Power;

fft.real=1;		// 1=Real FFT  0=complex FFT
fft.spectrum=1;		// 1=amplitude spectrum  2= Power spectrum
fft.normalize=1;	// 1=normalize magnitudes 0=leave unchanged
fft.shifted=0;		// 1=shift results  0=leave unshifted
fft.windowing=1;	// 1=rectangular
fft.unwrap=0;		// 1=unwrap  0=do not unwrap
fft.convention=1;	// 0=Engineering 1=science (this is the right property)

fft.forward( );		// Execute Forward FFT
window -c tmp;		// Close tmp worksheet --> disable this line to debug <--

quote:

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It's not clear from the fft documentation whether that value should be an exponent or a total number of points (n or 2^n). You might check it's value in the script window after running the FFT menu command. (I usually zero-fill prior to FFT and haven't paid much attention to this property.)

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