Programmer Guide/Command Reference/EVAL/ifft: Difference between revisions

From STX Wiki
Jump to navigationJump to search
No edit summary
No edit summary
 
(5 intermediate revisions by 3 users not shown)
Line 4: Line 4:
;Usage:<code>ifft(<var>x</var>, {, <var>xtype</var>, <var>poffset</var>, <var>prange</var>})</code>
;Usage:<code>ifft(<var>x</var>, {, <var>xtype</var>, <var>poffset</var>, <var>prange</var>})</code>
:;<var>x</var>: complex spectrum vector or matrix; if ''x'' is a matrix an inverse transform is computed for each column
:;<var>x</var>: complex spectrum vector or matrix; if ''x'' is a matrix an inverse transform is computed for each column
::*The spectra stored in ''x'' must be the 1st half of conj. sym. spectra, because a <code>complex->real</code> version of the inverse transformation is used and the results are real numbered signals.
::*The spectra stored in ''x'' must be the 1st half of conj. sym. spectra, because a <code>complex&rarr;real</code> version of the inverse transformation is used and the results are real numbered signals.
::*Each spectrum consists of <code>N=nrow(''x'')/2</code> complex values. The transformation length is set to <code>L=2*(N-1)</code>
::*Each spectrum consists of <code>N=nrow(''x'')/2</code> complex values. The transformation length is set to <code>L=2*(N-1)</code>
::*If the transformation length <code>L</code> is a power of 2 (<code>L=2^M</code>), the inverse '''fft''' algorithm is used, otherwise the inverse '''dft''' is used.
::*If the transformation length <code>L</code> is a power of 2 (<code>L=2^M</code>), the inverse '''fft''' algorithm is used, otherwise the inverse '''dft''' is used.
:;<var>xtype</var>: select the complex number format of ''x'' (default=0)
:;<var>xtype</var>: select the complex number format of ''x'' (default=0)
:::{|class="keinrahmen"
:::{|class="keinrahmen"
|''xtype''='''0''' ||-> cartesian <code>{ re, im, .. }</code>
|''xtype''='''0''' ||&rarr; cartesian <code>{ re, im, .. }</code>
|-
|-
|otherwise ||-> polar <code>{ amp, phase, .. }</code>
|otherwise ||&rarr; polar <code>{ amp, phase, .. }</code>
|}
|}
:;<var>poffset</var>: offset in samples to the signal begin or the selected ''zero phase'' position (default=0)
:;<var>poffset</var>: offset in samples to the signal begin or the selected ''zero phase'' position (default=0); If this value is not equal 0, the phase values stored in ''x'' are '''locked''' (see [[../fft|fft]]) and must be transformed to '''normal''' phase values before the inverse ft-transform is performed.
:If this value is not equal 0, the phase values stored in ''x'' are '''locked''' (see [[../fft|fft]]) and must be transformed to '''normal''' phase values before the inverse ft-transform is performed.
:;<var>prange</var>: selects the range of phase values stored in ''x'' (default=0)
:;<var>prange</var>: selects the range of phase values stored in ''x'' (default=0)
:::{|class="keinrahmen"
:::{|class="keinrahmen"
|''prange''='''0'' ||-> <code>0 <= phase[i] < 2*pi</code>
|''prange''='''0''' ||&rarr; <code>0 &le; phase[i] < 2*pi</code>
|-
|-
|otherwise ||-> <code>-pi <= phase[i] < pi</code>
|otherwise ||&rarr; <code>-pi &le; phase[i] < pi</code>
|}
|}
:*The arguments ''poffset'' and ''prange'' are ignored if ''xtype'' equals '''0''' (''x'' in cartesian format).
:*The arguments ''poffset'' and ''prange'' are ignored if ''xtype'' equals '''0''' (''x'' in cartesian format).
;Result 3: A matrix ''y'' with [[../ncol|ncol(''x'')]] columns, where each column ''y''[*,j] contains the result of the inverse transform (the real valued signal) of the column ''x''[*,j]. Each signal vector ''y''[*,j] consists of <code>L</code> (real) samples.
;Result: A matrix ''y'' with [[../ncol|ncol(''x'')]] columns, where each column ''y''[*,j] contains the result of the inverse transform (the real valued signal) of the column ''x''[*,j]. Each signal vector ''y''[*,j] consists of <code>L</code> (real) samples.
;See also: [[Programmer_Guide/Command_Reference/EVAL/fft|fft]], [[Programmer_Guide/Command_Reference/EVAL/dft|dft]], [[Programmer_Guide/Command_Reference/EVAL/dct|dct]], [[Programmer_Guide/Command_Reference/EVAL/cepstrum|cepstrum]], [[Programmer_Guide/Command_Reference/EVAL/lpc|lpc]], [[Programmer_Guide/Command_Reference/EVAL/complex arithmetic|complex arithmetic]]
;See also: [[../fft|fft]], [[../dft|dft]], [[../dct|dct]], [[../cepstrum|cepstrum]], [[../lpc|lpc]], [[../complex arithmetic|complex arithmetic]]


[[Programmer_Guide/Command_Reference/EVAL#Functions|<function list>]]
[[../#Functions|<function list>]]

Latest revision as of 10:56, 21 April 2011

Compute the inverse discrete fourier transform of a (conj. sym.) complex spectrum using the inverse fft or dft algorithm.

Usage
ifft(x, {, xtype, poffset, prange})
x
complex spectrum vector or matrix; if x is a matrix an inverse transform is computed for each column
  • The spectra stored in x must be the 1st half of conj. sym. spectra, because a complex→real version of the inverse transformation is used and the results are real numbered signals.
  • Each spectrum consists of N=nrow(x)/2 complex values. The transformation length is set to L=2*(N-1)
  • If the transformation length L is a power of 2 (L=2^M), the inverse fft algorithm is used, otherwise the inverse dft is used.
xtype
select the complex number format of x (default=0)
xtype=0 → cartesian { re, im, .. }
otherwise → polar { amp, phase, .. }
poffset
offset in samples to the signal begin or the selected zero phase position (default=0); If this value is not equal 0, the phase values stored in x are locked (see fft) and must be transformed to normal phase values before the inverse ft-transform is performed.
prange
selects the range of phase values stored in x (default=0)
prange=0 → 0 ≤ phase[i] < 2*pi
otherwise → -pi ≤ phase[i] < pi
  • The arguments poffset and prange are ignored if xtype equals 0 (x in cartesian format).
Result
A matrix y with ncol(x) columns, where each column y[*,j] contains the result of the inverse transform (the real valued signal) of the column x[*,j]. Each signal vector y[*,j] consists of L (real) samples.
See also
fft, dft, dct, cepstrum, lpc, complex arithmetic

<function list>

Retrieved from "https://mediawiki.kfs.oeaw.ac.at/stx/docs/wiki/index.php?title=Programmer_Guide/Command_Reference/EVAL/ifft&oldid=4034"

Navigation menu

Personal tools