function [dP] = GradJacobiP(r, alpha, beta, N);

% function [dP] = GradJacobiP(r, alpha, beta, N);
% Purpose: Evaluate the derivative of the Jacobi polynomial of type (alpha,beta)>-1,
%	       at points r for order N and returns dP[1:length(r))]        

  dP = zeros(length(r), 1);

  if(N == 0)
    dP(:,:) = 0.0;
  else
    dP = sqrt(N*(N+alpha+beta+1))*JacobiP(r(:),alpha+1,beta+1, N-1);
  end;

  return
end
