--- a
+++ b/cumtrapz.m
@@ -0,0 +1,98 @@
+## Copyright (C) 2000  Kai Habel
+##
+## 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, write to the Free Software
+## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{C} =} cumtrapz (@var{Y})
+## @deftypefnx {Function File} {@var{C} =} cumtrapz (@var{X},@var{Y})
+## 
+## cumulative numerical intergration using trapezodial method.
+## cumtrapz (@var{y}) computes the cumulative integral of the vector y.
+## If @var{y} is a matrix the integral is computed columnwise.
+## If the @var(X) argument is omitted a equally spaced vector is assumed. 
+## cumtrapz (@var{X},@var{Y}) evaluates the cumulative integral
+## with respect to @var{X}.
+##  
+## @seealso{trapz,cumsum}
+## @end deftypefn
+
+## Author:	Kai Habel <kai.habel@gmx.de>
+##
+## also: June 2000 Paul Kienzle (fixes,suggestions) 
+
+function C = cumtrapz (X, Y)
+
+  transposed = false;
+
+  if (nargin < 1) || (nargin > 2)
+    usage ("trapz (X, Y)");
+  elseif (nargin == 1)
+
+    if !(is_matrix (X))
+      error ("argument must be vector or matrix");
+    endif
+    
+    if (is_vector(X) && (rows (X) == 1))
+      ## row vector
+      X=X(:);
+      transposed = true; 
+    endif
+
+    r = rows(X);
+    C = zeros (size (X));
+
+    tmp = X(2:r, :) .+ X(1:r-1,:);
+
+    if (rows(tmp) == 1)
+      C(2,:) = 0.5 * tmp;
+    else
+      C(2:r,:) = 0.5 * cumsum (tmp);
+    endif
+    
+    if (transposed) C = C'; endif
+
+  elseif (nargin == 2)
+
+    if !(is_matrix (X) && is_matrix (Y))
+      error ("arguments must be vectors or matrices of same size");
+    endif
+
+    if (size (X) == size (Y'))
+      X = X';
+    elseif (size (X) != size (Y))
+      error ("X and Y must have same shape");
+    endif
+
+    if (is_vector (Y) && (rows (Y) == 1))
+      ## Y is row vector
+      X = X (:); Y = Y (:);
+      transposed = true;
+    endif
+
+    r = rows (Y);
+    C = zeros (size (Y));
+
+    tmp = (X(2:r, :) .- X(1:r-1,:)) .* (Y(2:r,:) .+ Y(1:r - 1, :));
+
+    if (rows(tmp) == 1)
+      C(2,:) = 0.5 *tmp;
+    else
+      C(2:r,:) = 0.5 * cumsum (tmp);
+    endif
+
+    if (transposed) C = C'; endif
+
+  endif
+endfunction