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Version:
4.4.5.dfsg-3ubuntu2 ▾
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<HTML>
<HEAD>
<TITLE>Inverse fast Fourier transform</TITLE>
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<BODY bgcolor="#FFFFFF" fgcolor="#000000">
<P><font size="+3" color="green"><B>Inverse fast Fourier transform</B></font></P>
<P>
<TABLE border="1" cols="2" frame="box" rules="all" width="572">
<TR>
<TD width="15%" valign="top"><B>Syntax</B>:</TD>
<TD width="85%"><CODE>
y = IFFT(m)<br />
y = IFFT(m,'AMP&PHASE')<br />
y = IFFT(m,'COS&SIN')</CODE>
</TD></TR>
</table></p>
<p>
The <CODE>IFFT</CODE> function calculates the
inverse discrete Fourier transform of the two column input matrix. This matrix is
usually calculated by the <CODE><a href="fft.htm">FFT</a></CODE> function, thus
reconstructing the original data.</p>
<p>
By default, <CODE>IFFT</CODE> expects amplitudes and phases,
where the phases are in degrees. The first column of the matrix should contain the amplitudes
and the second column the phases. If the <CODE>COS&SIN</CODE>
keyword is used, <CODE>IFFT</CODE> expects the Fourier coefficients,
that is, the cosine coefficients in the first column and the sine coefficients in the second
column. If the input matrix has <code>N</code> rows, the function returns a vector with
length <code>2(N-1)</code>.</p>
<p>
The principle usage of the <CODE>IFFT</CODE> function is to
modify some of the amplitudes returned from the <CODE>FFT</CODE>
function and note their effect on the original data. A typical application would be
one of data smoothing, in which the user would zero out the amplitudes of the higher order
harmonics.</p>
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