function u=shapefunction_2D4N(chi,unod)
	%unod ('u' at nodes) is a column vector
    %chi=[chi(1) chi(2)]=[ji nu]
    ji=chi(1);nu=chi(2);
	[numdofs filas]=size(unod);	
	N1=.25*(1-ji)*(1-nu);
	N2=.25*(1+ji)*(1-nu);
	N3=.25*(1+ji)*(1+nu);
	N4=.25*(1-ji)*(1+nu);
	if(numdofs==4) %u is 1D function
	u=[N1 N2 N3 N4]*unod;
	elseif(numdofs==8) %u is 1D function
	u=[N1 0 N2 0 N3 0 N4 0;0 N1 0 N2 0 N3 0 N4]*unod;
	elseif(numdofs==6) %u is 1D function
	u=[N1 0 0 N2 0 0 N3 0 0 N4 0 0;0 N1 0 0 N2 0 0 N3 0 0 N4 0; 0 0 N1 0 0 N2 0 0 N3 0 0 N4]*unod;
	end
return