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Info_Mac IV CD-ROM (Pacific HiTech Inc.)(August 1994).iso
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faxis.r
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1994-04-25
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//---------------------------------------------------------------------------
// faxis.r
// Syntax: faxis ( X )
// faxis ( X , T )
// faxis ( X , T, axis_type )
// Description:
// Faxis generates a frequency axis for FFT plots.
//
// X = FFT data
// T = sampling period (optional argument)
// axis_type = type of axis to create:
// 1 = Digital Rad/s [0,2pi], 2 = Analog Radians/s
// 3 = Analog Hertz 4 = Normalized frequency [0,2]
//
// Defaults if not specified: T = 1, axis_type = 1
//
//---------------------------------------------------------------------------
faxis = function ( X, _T, axis_type )
{
local (a, N, T)
if (!exist (axis_type)) { axis_type = 1; }
if (!exist (_T)) { T = 1; axis_type = 1; else T = _T; }
N = length (X);
a = (0:N-1)/N;
a = reshape (a, X.nr, X.nc);
if (axis_type == 3)
{
a = a/T;
else if (axis_type == 2) {
a = a * (2*pi/T);
else if (axis_type == 4) {
a = 2 * a;
else
a = a * (2*pi);
}}}
return a
};