Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / signal-1.1.3 / cheb.m

diff --git a/octave_packages/signal-1.1.3/cheb.m b/octave_packages/signal-1.1.3/cheb.m
new file mode 100644 (file)
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+++ b/octave_packages/signal-1.1.3/cheb.m
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+## Copyright (C) 2002 André Carezia <acarezia@uol.com.br>
+##
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## Usage:  cheb (n, x)
+##
+## Returns the value of the nth-order Chebyshev polynomial calculated at
+## the point x. The Chebyshev polynomials are defined by the equations:
+##
+##           / cos(n acos(x),    |x| <= 1
+##   Tn(x) = |
+##           \ cosh(n acosh(x),  |x| > 1
+##
+## If x is a vector, the output is a vector of the same size, where each
+## element is calculated as y(i) = Tn(x(i)).
+
+function T = cheb (n, x)
+  if (nargin != 2)
+    print_usage;
+  elseif !(isscalar (n) && (n == round(n)) && (n >= 0))
+    error ("cheb: n has to be a positive integer");
+  endif
+
+  if (max(size(x)) == 0)
+    T = [];
+  endif
+        # avoid resizing latencies
+  T = zeros(size(x));
+  ind = abs (x) <= 1;
+  if (max(size(ind)))
+    T(ind) = cos(n*acos(x(ind)));
+  endif
+
+  ind = abs (x) > 1;
+  if (max(size(ind)))
+    T(ind) = cosh(n*acosh(x(ind)));
+  endif
+
+  T = real(T);
+endfunction