\(\newcommand{\W}[1]{ \; #1 \; }\) \(\newcommand{\R}[1]{ {\rm #1} }\) \(\newcommand{\B}[1]{ {\bf #1} }\) \(\newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} }\) \(\newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} }\) \(\newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} }\) \(\newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }\)

det_by_minor.cpp

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Determinant Using Expansion by Minors: Example and Test

# include <cppad/cppad.hpp>
# include <cppad/speed/det_by_minor.hpp>

bool det_by_minor()
{  bool ok = true;

   // dimension of the matrix
   size_t n = 3;

   // construct the determinat object
   CppAD::det_by_minor<double> Det(n);

   double  a[] = {
      1., 2., 3.,  // a[0] a[1] a[2]
      3., 2., 1.,  // a[3] a[4] a[5]
      2., 1., 2.   // a[6] a[7] a[8]
   };
   CPPAD_TESTVECTOR(double) A(9);
   size_t i;
   for(i = 0; i < 9; i++)
      A[i] = a[i];


   // evaluate the determinant
   double det = Det(A);

   double check;
   check = a[0]*(a[4]*a[8] - a[5]*a[7])
          - a[1]*(a[3]*a[8] - a[5]*a[6])
          + a[2]*(a[3]*a[7] - a[4]*a[6]);

   ok = det == check;

   return ok;
}