Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / fixed-0.7.10 / lookup_table.m

diff --git a/octave_packages/fixed-0.7.10/lookup_table.m b/octave_packages/fixed-0.7.10/lookup_table.m
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+## Copyright (C) 2003  Motorola Inc
+## Copyright (C) 2003  David Bateman
+##
+## 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 2 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/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{y} =} lookup_table (@var{table}, @var{x})
+## @deftypefnx {Function File} {@var{y} =} lookup_table (@var{table}, @var{x}, @var{interp}, @var{extrap})
+## Using the lookup table created by @dfn{create_lookup_table}, find the value
+## @var{y} corresponding to @var{x}. With two arguments the lookup is done
+## to the nearest value below in the table less than the desired value. With
+## three arguments a simple linear interpolation is performed. With four
+## arguments an extrapolation is also performed. The exact values of arguments
+## three and four are irrelevant, as only there presence detremines whether
+## interpolation and/or extrapolation are used.
+## @end deftypefn
+
+function y = lookup_table (table, x, interp, extrap);
+  if (nargin < 2)
+    error("lookup_table: needs two or more arguments");
+  else 
+    idx = lookup(table.x, x);
+    if (nargin == 2)
+      y = table.y (max(1,idx));
+    else
+      len = length(table.x);
+      before = find(idx == 0);
+      after = find(idx == len);
+      idx = max(1,min(idx, len-1));
+      xl = table.x(idx);
+      yl = table.y(idx);
+      xu = table.x(idx+1);
+      yu = table.y(idx+1);
+      ## Careful with the order of this interpolation to avoid underflow
+      ## in fixed point calculations.
+      y = ( yl + (yu - yl) ./ (xu - xl) .* (x - xl));
+      if (nargin < 4)
+       y(before) = table.y(1);
+       y(after) = table.y(len);
+      endif
+    endif
+  endif
+endfunction