// Polynomes de Lagrange Q_1 et derivees fonction de forme et derivees
// evaluees au point (x,y)
//
function [FP,DxFP,DyFP] = Q1(x,y)
// 
  FP = zeros(4,1);   DxFP = zeros(4,1); DyFP = zeros(4,1);
//
  FP(1,1) =  (1-x)*(1-y)/4;
  FP(2,1) =  (1+x)*(1-y)/4;
  FP(3,1) =  (1+x)*(1+y)/4;
  FP(4,1) =  (1-x)*(1+y)/4;


  DxFP(1,1) = -(1-y)/4;
  DxFP(2,1) =  (1-y)/4;
  DxFP(3,1) =  (1+y)/4;
  DxFP(4,1) = -(1+y)/4;


  DyFP(1,1) = -(1-x)/4;
  DyFP(2,1) = -(1+x)/4;
  DyFP(3,1) =  (1+x)/4;
  DyFP(4,1) =  (1-x)/4;


endfunction


