thank you a lot, you solved my problem !

i only want to draw the contour of my function.

carte:=proc(deph::Array,n)
local r,alpha,S;  
S:=(r,alpha)->sum(exp(I*r+I*(deph[i]-alpha)), i = 1 .. n)
contourplot(abs(S(r,alpha)),r=0..15*lambda,alpha=0..2*Pi,coords=cylindrical,numpoints=10000,axes=none,style=patchnogrid);
end;


actually, i now have 1 more problem : the proc doesn't work anymore, and maple shows : "Error, (in S) bad index into Array"

gerald

ok, i give you my proc :

r:=proc (R::array, theta::array,n)
local ...
deph:=array(1..n);        <- these are my vars
S:= (deph) -> sum( exp ( I*deph[i] );

end;