function?y=lagrange（xpointxpointy）
%
%LAGRANGE???approx?a?point-defined?function?using?the?Lagrange?polynomial?interpolation
%
%??????LAGRANGE（XPOINTXPOINTY）?approx?the?function?definited?by?the?points:
%??????P1=（POINTX（1）POINTY（1））?P2=（POINTX（2）POINTY（2））?...?PN（POINTX（N）POINTY（N））
%??????and?calculate?it?in?each?elements?of?X
%
%??????If?POINTX?and?POINTY?have?different?number?of?elements?the?function?will?return?the?NaN?value
%
%??????function?wrote?by:?Calzino
%??????7-oct-2001
%
n=size（pointx2）;
L=ones（nsize（x2））;
if?（size（pointx2）~=size（pointy2））
???fprintf（1‘\nERROR!\nPOINTX?and?POINTY?must?have?the?same?number?of?elements\n‘）;
???y=NaN;
else
???for?i=1:n
??????for?j=1:n
?????????if?（i~=j）
????????????L（i:）=L（i:）.*（x-pointx（j））/（pointx（i）-pointx（j））;
?????????end
??????end
???end
???y=0;
???for?i=1:n
??????y=y+pointy（i）*L（i:）;
???end
end