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+// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
+// Copyright (C) 1991 - INRIA - Serge Steer
+// This file must be used under the terms of the CeCILL.
+// This source file is licensed as described in the file COPYING, which
+// you should have received as part of this distribution.  The terms
+// are also available at
+// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt
+
+function d=projaff(x,y,pt)
+    // projaff - projection d'un point sur une droite
+    //%Syntaxe
+    // d=projaff(x,y,pt)
+    //%Parametres
+    // x: vecteur des abscisses des 2 points definissant la droite
+    // y: vecteur des ordonnes des 2 points definissant la droite
+    // pt: coordonnes du point a projeter [abscisses ordonnees]
+    //%Methode
+    //l'equation de la droite est :
+    //(y2-y1)*(x-x1)-(x2-x1)*(y-y1)=0
+    //celle de la normale passant par le point:
+    //(x2-x1)*(x-xp)+(y2-y1)*(y-yp)=0
+    //
+    //!
+
+    if argn(2)<>3 then
+        error(msprintf(gettext("%s: Wrong number of input argument(s): %d expected.\n"), "projaff", 3));
+    end
+
+    dx=x(2)-x(1);dy=y(2)-y(1)
+    m=[dy -dx;dx dy]
+    d=m\ [-x(2)*y(1)+x(1)*y(2);m(2,:)*[pt(1);pt(2)]]
+endfunction