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@(@\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }@)@
Sparse Jacobian: Example and Test

# include <cppad/cppad.hpp>
namespace { // ---------------------------------------------------------
bool reverse()
{     bool ok = true;
     using CppAD::AD;
     using CppAD::NearEqual;
     typedef CPPAD_TESTVECTOR(AD<double>)   a_vector;
     typedef CPPAD_TESTVECTOR(double)       d_vector;
     typedef CPPAD_TESTVECTOR(size_t)       i_vector;
     size_t i, j, k, ell;
     double eps = 10. * CppAD::numeric_limits<double>::epsilon();

     // domain space vector
     size_t n = 4;
     a_vector  a_x(n);
     for(j = 0; j < n; j++)
          a_x[j] = AD<double> (0);

     // declare independent variables and starting recording
     CppAD::Independent(a_x);

     size_t m = 3;
     a_vector  a_y(m);
     a_y[0] = a_x[0] + a_x[1];
     a_y[1] = a_x[2] + a_x[3];
     a_y[2] = a_x[0] + a_x[1] + a_x[2] + a_x[3] * a_x[3] / 2.;

     // create f: x -> y and stop tape recording
     CppAD::ADFun<double> f(a_x, a_y);

     // new value for the independent variable vector
     d_vector x(n);
     for(j = 0; j < n; j++)
          x[j] = double(j);

     // Jacobian of y without sparsity pattern
     d_vector jac(m * n);
     jac = f.SparseJacobian(x);
     /*
           [ 1 1 0 0  ]
     jac = [ 0 0 1 1  ]
           [ 1 1 1 x_3]
     */
     d_vector check(m * n);
     check[0] = 1.; check[1] = 1.; check[2]  = 0.; check[3]  = 0.;
     check[4] = 0.; check[5] = 0.; check[6]  = 1.; check[7]  = 1.;
     check[8] = 1.; check[9] = 1.; check[10] = 1.; check[11] = x[3];
     for(ell = 0; ell < size_t(check.size()); ell++)
          ok &=  NearEqual(check[ell], jac[ell], eps, eps );

     // using packed boolean sparsity patterns
     CppAD::vectorBool s_b(m * m), p_b(m * n);
     for(i = 0; i < m; i++)
     {     for(ell = 0; ell < m; ell++)
               s_b[i * m + ell] = false;
          s_b[i * m + i] = true;
     }
     p_b   = f.RevSparseJac(m, s_b);
     jac   = f.SparseJacobian(x, p_b);
     for(ell = 0; ell < size_t(check.size()); ell++)
          ok &=  NearEqual(check[ell], jac[ell], eps, eps );

     // using vector of sets sparsity patterns
     std::vector< std::set<size_t> > s_s(m),  p_s(m);
     for(i = 0; i < m; i++)
          s_s[i].insert(i);
     p_s   = f.RevSparseJac(m, s_s);
     jac   = f.SparseJacobian(x, p_s);
     for(ell = 0; ell < size_t(check.size()); ell++)
          ok &=  NearEqual(check[ell], jac[ell], eps, eps );

     // using row and column indices to compute non-zero in rows 1 and 2
     // (skip row 0).
     size_t K = 6;
     i_vector row(K), col(K);
     jac.resize(K);
     k = 0;
     for(j = 0; j < n; j++)
     {     for(i = 1; i < m; i++)
          {     ell = i * n + j;
               if( p_b[ell] )
               {     ok &= check[ell] != 0.;
                    row[k] = i;
                    col[k] = j;
                    k++;
               }
          }
     }
     ok &= k == K;

     // empty work structure
     CppAD::sparse_jacobian_work work;

     // could use p_b
     size_t n_sweep = f.SparseJacobianReverse(x, p_s, row, col, jac, work);
     for(k = 0; k < K; k++)
     {     ell = row[k] * n + col[k];
          ok &= NearEqual(check[ell], jac[k], eps, eps);
     }
     ok &= n_sweep == 2;

     // now recompute at a different x value (using work from previous call)
     check[11] = x[3] = 10.;
     std::vector< std::set<size_t> > not_used;
     n_sweep = f.SparseJacobianReverse(x, not_used, row, col, jac, work);
     for(k = 0; k < K; k++)
     {     ell = row[k] * n + col[k];
          ok &= NearEqual(check[ell], jac[k], eps, eps);
     }
     ok &= n_sweep == 2;

     return ok;
}

bool forward()
{     bool ok = true;
     using CppAD::AD;
     using CppAD::NearEqual;
     typedef CPPAD_TESTVECTOR(AD<double>) a_vector;
     typedef CPPAD_TESTVECTOR(double)       d_vector;
     typedef CPPAD_TESTVECTOR(size_t)       i_vector;
     size_t i, j, k, ell;
     double eps = 10. * CppAD::numeric_limits<double>::epsilon();

     // domain space vector
     size_t n = 3;
     a_vector  a_x(n);
     for(j = 0; j < n; j++)
          a_x[j] = AD<double> (0);

     // declare independent variables and starting recording
     CppAD::Independent(a_x);

     size_t m = 4;
     a_vector  a_y(m);
     a_y[0] = a_x[0] + a_x[2];
     a_y[1] = a_x[0] + a_x[2];
     a_y[2] = a_x[1] + a_x[2];
     a_y[3] = a_x[1] + a_x[2] * a_x[2] / 2.;

     // create f: x -> y and stop tape recording
     CppAD::ADFun<double> f(a_x, a_y);

     // new value for the independent variable vector
     d_vector x(n);
     for(j = 0; j < n; j++)
          x[j] = double(j);

     // Jacobian of y without sparsity pattern
     d_vector jac(m * n);
     jac = f.SparseJacobian(x);
     /*
           [ 1 0 1   ]
     jac = [ 1 0 1   ]
           [ 0 1 1   ]
           [ 0 1 x_2 ]
     */
     d_vector check(m * n);
     check[0] = 1.; check[1]  = 0.; check[2]  = 1.;
     check[3] = 1.; check[4]  = 0.; check[5]  = 1.;
     check[6] = 0.; check[7]  = 1.; check[8]  = 1.;
     check[9] = 0.; check[10] = 1.; check[11] = x[2];
     for(ell = 0; ell < size_t(check.size()); ell++)
          ok &=  NearEqual(check[ell], jac[ell], eps, eps );

     // test using packed boolean vectors for sparsity pattern
     CppAD::vectorBool r_b(n * n), p_b(m * n);
     for(j = 0; j < n; j++)
     {     for(ell = 0; ell < n; ell++)
               r_b[j * n + ell] = false;
          r_b[j * n + j] = true;
     }
     p_b = f.ForSparseJac(n, r_b);
     jac = f.SparseJacobian(x, p_b);
     for(ell = 0; ell < size_t(check.size()); ell++)
          ok &=  NearEqual(check[ell], jac[ell], eps, eps );

     // test using vector of sets for sparsity pattern
     std::vector< std::set<size_t> > r_s(n), p_s(m);
     for(j = 0; j < n; j++)
          r_s[j].insert(j);
     p_s = f.ForSparseJac(n, r_s);
     jac = f.SparseJacobian(x, p_s);
     for(ell = 0; ell < size_t(check.size()); ell++)
          ok &=  NearEqual(check[ell], jac[ell], eps, eps );

     // using row and column indices to compute non-zero elements excluding
     // row 0 and column 0.
     size_t K = 5;
     i_vector row(K), col(K);
     jac.resize(K);
     k = 0;
     for(i = 1; i < m; i++)
     {     for(j = 1; j < n; j++)
          {     ell = i * n + j;
               if( p_b[ell] )
               {     ok &= check[ell] != 0.;
                    row[k] = i;
                    col[k] = j;
                    k++;
               }
          }
     }
     ok &= k == K;

     // empty work structure
     CppAD::sparse_jacobian_work work;

     // could use p_s
     size_t n_sweep = f.SparseJacobianForward(x, p_b, row, col, jac, work);
     for(k = 0; k < K; k++)
     {    ell = row[k] * n + col[k];
          ok &= NearEqual(check[ell], jac[k], eps, eps);
     }
     ok &= n_sweep == 2;

     // now recompute at a different x value (using work from previous call)
     check[11] = x[2] = 10.;
     n_sweep = f.SparseJacobianForward(x, p_s, row, col, jac, work);
     for(k = 0; k < K; k++)
     {    ell = row[k] * n + col[k];
          ok &= NearEqual(check[ell], jac[k], eps, eps);
     }
     ok &= n_sweep == 2;

     return ok;
}
} // End empty namespace

bool sparse_jacobian(void)
{     bool ok = true;
     ok &= forward();
     ok &= reverse();

     return ok;
}

Input File: example/sparse/sparse_jacobian.cpp