#include <stan/math/rev/mat.hpp>
#include <gtest/gtest.h>
#include <test/unit/math/rev/mat/fun/util.hpp>

TEST(AgradRevMatrix,eigenval_sum) {
  using stan::math::sum;
  using stan::math::matrix_v;
  using stan::math::vector_v;
  using stan::math::eigenvalues_sym;

  matrix_v a(3,3);
  a << 
    1.0, 2.0, 3.0,
    2.0, 5.0, 7.9,
    3.0, 7.9, 1.08;
  AVEC x = createAVEC(a(0,0), a(1,1), a(2,2), a(1,2));
  x.push_back(a(0,1));
  x.push_back(a(2,0));

  // grad sum eig = I
  vector_v a_eigenvalues = eigenvalues_sym(a);
  
  AVAR sum_a_eigenvalues = sum(a_eigenvalues);
  
  VEC g = cgradvec(sum_a_eigenvalues,x);

  EXPECT_NEAR(1.0,g[0],1.0E-11);
  EXPECT_NEAR(1.0,g[1],1.0E-11);
  EXPECT_NEAR(1.0,g[2],1.0E-11);

  EXPECT_NEAR(0.0,g[3],1.0E-10);
  EXPECT_NEAR(0.0,g[4],1.0E-10);
  EXPECT_NEAR(0.0,g[5],1.0E-10);
}
