--- a/scripts/plot/contour.m
+++ b/scripts/plot/contour.m
@@ -1,4 +1,4 @@
-## Copyright (C) 1996, 1997 John W. Eaton
+## Copyright (C) 1996, 1997, 2002 John W. Eaton
 ##
 ## This file is part of Octave.
 ##
@@ -54,60 +54,78 @@
           tmp = sprintf ("%s, %f", tmp, n(i));
         endfor
         command = sprintf ("gset cntrparam levels discrete %s", tmp);
+      else
+	error ("contour: levels must be a scalar or vector") ;
       endif
       eval (command);
       gset noparametric;
       gset view 0, 0, 1, 1;
       gsplot z w l 1;
     else
-      error ("contour: argument must be a matrix");
+      error ("contour: z of contour (z, levels) must be a matrix");
     endif
   elseif (nargin == 3 || nargin == 4)
     if (nargin == 3)
       n = 10;
     endif
-    if (isvector (x) && isvector (y) && ismatrix (z))
-      xlen = length (x);
-      ylen = length (y);
-      if (xlen == columns (z) && ylen == rows (z))
-        if (rows (x) == 1)
-          x = x';
-        endif
-        len = 3 * ylen;
-        zz = zeros (xlen, len);
-        k = 1;
-        for i = 1:3:len
-          zz(:,i)   = x;
-          zz(:,i+1) = y(k) * ones (xlen, 1);
-          zz(:,i+2) = z(k,:)';
-          k++;
+    if (ismatrix (z))
+      size_msg = ["contour: columns(z) must be the same as length(x) and\n" \
+		  "rows(z) must be the same as length(y),\n" \
+		  "or x, y, and z must be matrices with the same size"];
+      if (isvector (x) && isvector (y))
+	xlen = length (x);
+	ylen = length (y);
+	if (xlen == columns (z) && ylen == rows (z))
+          if (rows (x) == 1)
+            x = x';
+          endif
+          len = 3 * ylen;
+          zz = zeros (xlen, len);
+          k = 1;
+          for i = 1:3:len
+            zz(:,i)   = x;
+            zz(:,i+1) = y(k) * ones (xlen, 1);
+            zz(:,i+2) = z(k,:)';
+            k++;
+          endfor
+	else
+          error (size_msg);
+	endif
+      else
+	z_size = size (z);
+	if (z_size == size (x) && z_size == size (y))
+	  nc = 3*z_size(1);
+	  zz = zeros (z_size(2), nc);
+	  zz(:,1:3:nc) = x';
+	  zz(:,2:3:nc) = y';
+	  zz(:,3:3:nc) = z';
+	else
+	  error (size_msg);
+	endif
+      endif
+      gset nosurface;
+      gset contour;
+      gset cntrparam bspline;
+      if (isscalar (n))
+        command = sprintf ("gset cntrparam levels %d", n);
+      elseif (isvector (n))
+        tmp = sprintf ("%f", n(1));
+        for i = 2:length (n)
+          tmp = sprintf ("%s, %f", tmp, n(i));
         endfor
-        gset nosurface;
-        gset contour;
-        gset cntrparam bspline;
-        if (isscalar (n))
-          command = sprintf ("gset cntrparam levels %d", n);
-        elseif (isvector (n))
-          tmp = sprintf ("%f", n(1));
-          for i = 2:length (n)
-            tmp = sprintf ("%s, %f", tmp, n(i));
-          endfor
-          command = sprintf ("gset cntrparam levels discrete %s", tmp);
-        endif
-        eval (command);
-        gset parametric;
-        gset view 0, 0, 1, 1;
-        gsplot zz w l 1;
+        command = sprintf ("gset cntrparam levels discrete %s", tmp);
       else
-        msg = "contour: rows (z) must be the same as length (x) and";
-        msg = sprintf ("%s\ncolumns (z) must be the same as length (y)", msg);
-        error (msg);
+	error ("contour: levels must be a scalar or vector") ;
       endif
+      eval (command);
+      gset parametric;
+      gset view 0, 0, 1, 1;
+      gsplot zz w l 1;
     else
       error ("contour: x and y must be vectors and z must be a matrix");
     endif
   else
-    usage ("contour (z, x, y, levels)");
+    usage ("contour (x, y, z, levels) or contour (z, levels)");
   endif
 
 endfunction