function [p] = pmatrix( n , nbig)
%  builds the matrix P, see formula 2.38 of SISC article, dim p=n X nbig
for i=2:n
    delta(i)=sqrt(2./n);
end
%%%%%%%%%%%%%%%%%%%%% computing the nodes of the quadrature
s=wnodes(nbig);
delta(1)=sqrt(1./n);
for i=1:n
    for j=1:nbig
        p(i,j)=delta(i)*cos((i-1)*acos(s(j)));
    end
end
end

