function [ u, dudx, dudy ] = solution_evaluate ( xy, t, node_u )

%% SOLUTION_EVALUATE evaluates the solution at a point in a triangle.
%
%  Modified:
%
%    24 June 2004
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, real XY(2), the point at which the solution is to be evaluated.
%
%    Input, real T(2,3), the coordinates of the vertices of the triangle containing XY.
%
%    Input, real NODE_U(3), the value of the finite element coefficients at the vertices.
%
  u = 0.0;
  dudx = 0.0;
  dudy = 0.0;

  for i = 1 : 3

    [ b, dbdy, dbdy ] = basis_all_t3 ( t, i, xy );

    u    = u    + node_u(i) * b;
    dudx = dudx + node_u(i) * dbdx;
    dudy = dudy + node_u(i) * dbdy;

  end