function prod=prod(x)
%-----------------------------------------------------------------------
% For i>0, return the product of a set of given basis functions.
% For i=0, return the function values.
% Input x is a row vector
%-----------------------------------------------------------------------

      global i j

      f = [ besselj(0,x); besselj(0,2*x); besselj(0,3*x); besselj(0,4*x); besselj(0,5*x) ];
      if i>0
        prod = f(i,:).*f(j,:);
%       prod = besselj(0,lambda(i)*x) .* besselj(0,lambda(j)*x);
      else
        prod=f;
      end