CPPLapack Code

typedef dgematrix_small<3,3> dgemat3;

//=============================================================================
/*! calculate determinant */
inline double det(const dgemat3& A)
{
  return
    +A(0,0)*A(1,1)*A(2,2) -A(0,0)*A(1,2)*A(2,1)
    +A(0,1)*A(1,2)*A(2,0) -A(0,1)*A(1,0)*A(2,2)
    +A(0,2)*A(1,0)*A(2,1) -A(0,2)*A(1,1)*A(2,0);
}

//=============================================================================
/*! calculate inverse */
inline dgemat3 inv(const dgemat3& A)
{
  const double Adet( det(A) );
  dgemat3 Ainv;
  Ainv(0,0)=(A(1,1)*A(2,2)-A(1,2)*A(2,1))/Adet;
  Ainv(0,1)=(A(0,2)*A(2,1)-A(0,1)*A(2,2))/Adet;
  Ainv(0,2)=(A(0,1)*A(1,2)-A(0,2)*A(1,1))/Adet;
  Ainv(1,0)=(A(1,2)*A(2,0)-A(1,0)*A(2,2))/Adet;
  Ainv(1,1)=(A(0,0)*A(2,2)-A(0,2)*A(2,0))/Adet;
  Ainv(1,2)=(A(0,2)*A(1,0)-A(0,0)*A(1,2))/Adet;
  Ainv(2,0)=(A(1,0)*A(2,1)-A(1,1)*A(2,0))/Adet;
  Ainv(2,1)=(A(0,1)*A(2,0)-A(0,0)*A(2,1))/Adet;
  Ainv(2,2)=(A(0,0)*A(1,1)-A(0,1)*A(1,0))/Adet;
  return Ainv;
}