nonsymmv.c

来自「math library from gnu」· C语言 代码 · 共 970 行 · 第 1/3 页

         ii;
  gsl_complex lambda; /* current eigenvalue */
  double lambda_re,   /* Re(lambda) */
         lambda_im;   /* Im(lambda) */
  gsl_matrix_view Tv, /* temporary views */
                  Zv;
  gsl_vector_view y,  /* temporary views */
                  y2,
                  ev,
                  ev2;
  double dat[4],      /* scratch arrays */
         dat_X[4];
  double scale;       /* scale factor */
  double xnorm;       /* |X| */
  gsl_vector_complex_view ecol, /* column of evec */
                          ecol2;
  int complex_pair;   /* complex eigenvalue pair? */
  double smin;

  /*
   * Compute 1-norm of each column of upper triangular part of T
   * to control overflow in triangular solver
   */

  gsl_vector_set(w->work3, 0, 0.0);
  for (ju = 1; ju < N; ++ju)
    {
      gsl_vector_set(w->work3, ju, 0.0);
      for (iu = 0; iu < ju; ++iu)
        {
          gsl_vector_set(w->work3, ju,
                         gsl_vector_get(w->work3, ju) +
                         fabs(gsl_matrix_get(T, iu, ju)));
        }
    }

  for (i = (int) N - 1; i >= 0; --i)
    {
      iu = (size_t) i;

      /* get current eigenvalue and store it in lambda */
      lambda_re = gsl_matrix_get(T, iu, iu);

      if (iu != 0 && gsl_matrix_get(T, iu, iu - 1) != 0.0)
        {
          lambda_im = sqrt(fabs(gsl_matrix_get(T, iu, iu - 1))) *
                      sqrt(fabs(gsl_matrix_get(T, iu - 1, iu)));
        }
      else
        {
          lambda_im = 0.0;
        }

      GSL_SET_COMPLEX(&lambda, lambda_re, lambda_im);

      smin = GSL_MAX(GSL_DBL_EPSILON * (fabs(lambda_re) + fabs(lambda_im)),
                     smlnum);
      smin = GSL_MAX(smin, GSL_NONSYMMV_SMLNUM);

      if (lambda_im == 0.0)
        {
          int k, l;
          gsl_vector_view bv, xv;

          /* real eigenvector */

          /*
           * The ordering of eigenvalues in 'eval' is arbitrary and
           * does not necessarily follow the Schur form T, so store
           * lambda in the right slot in eval to ensure it corresponds
           * to the eigenvector we are about to compute
           */
          gsl_vector_complex_set(eval, iu, lambda);

          /*
           * We need to solve the system:
           *
           * (T(1:iu-1, 1:iu-1) - lambda*I)*X = -T(1:iu-1,iu)
           */

          /* construct right hand side */
          for (k = 0; k < i; ++k)
            {
              gsl_vector_set(w->work,
                             (size_t) k,
                             -gsl_matrix_get(T, (size_t) k, iu));
            }

          gsl_vector_set(w->work, iu, 1.0);

          for (l = i - 1; l >= 0; --l)
            {
              size_t lu = (size_t) l;

              if (lu == 0)
                complex_pair = 0;
              else
                complex_pair = gsl_matrix_get(T, lu, lu - 1) != 0.0;

              if (!complex_pair)
                {
                  double x;

                  /*
                   * 1-by-1 diagonal block - solve the system:
                   *
                   * (T_{ll} - lambda)*x = -T_{l(iu)}
                   */

                  Tv = gsl_matrix_submatrix(T, lu, lu, 1, 1);
                  bv = gsl_vector_view_array(dat, 1);
                  gsl_vector_set(&bv.vector, 0,
                                 gsl_vector_get(w->work, lu));
                  xv = gsl_vector_view_array(dat_X, 1);

                  gsl_schur_solve_equation(1.0,
                                           &Tv.matrix,
                                           lambda_re,
                                           1.0,
                                           1.0,
                                           &bv.vector,
                                           &xv.vector,
                                           &scale,
                                           &xnorm,
                                           smin);

                  /* scale x to avoid overflow */
                  x = gsl_vector_get(&xv.vector, 0);
                  if (xnorm > 1.0)
                    {
                      if (gsl_vector_get(w->work3, lu) > bignum / xnorm)
                        {
                          x /= xnorm;
                          scale /= xnorm;
                        }
                    }

                  if (scale != 1.0)
                    {
                      gsl_vector_view wv;

                      wv = gsl_vector_subvector(w->work, 0, iu + 1);
                      gsl_blas_dscal(scale, &wv.vector);
                    }

                  gsl_vector_set(w->work, lu, x);

                  if (lu > 0)
                    {
                      gsl_vector_view v1, v2;

                      /* update right hand side */

                      v1 = gsl_matrix_subcolumn(T, lu, 0, lu);
                      v2 = gsl_vector_subvector(w->work, 0, lu);
                      gsl_blas_daxpy(-x, &v1.vector, &v2.vector);
                    } /* if (l > 0) */
                } /* if (!complex_pair) */
              else
                {
                  double x11, x21;

                  /*
                   * 2-by-2 diagonal block
                   */

                  Tv = gsl_matrix_submatrix(T, lu - 1, lu - 1, 2, 2);
                  bv = gsl_vector_view_array(dat, 2);
                  gsl_vector_set(&bv.vector, 0,
                                 gsl_vector_get(w->work, lu - 1));
                  gsl_vector_set(&bv.vector, 1,
                                 gsl_vector_get(w->work, lu));
                  xv = gsl_vector_view_array(dat_X, 2);

                  gsl_schur_solve_equation(1.0,
                                           &Tv.matrix,
                                           lambda_re,
                                           1.0,
                                           1.0,
                                           &bv.vector,
                                           &xv.vector,
                                           &scale,
                                           &xnorm,
                                           smin);

                  /* scale X(1,1) and X(2,1) to avoid overflow */
                  x11 = gsl_vector_get(&xv.vector, 0);
                  x21 = gsl_vector_get(&xv.vector, 1);

                  if (xnorm > 1.0)
                    {
                      double beta;

                      beta = GSL_MAX(gsl_vector_get(w->work3, lu - 1),
                                     gsl_vector_get(w->work3, lu));
                      if (beta > bignum / xnorm)
                        {
                          x11 /= xnorm;
                          x21 /= xnorm;
                          scale /= xnorm;
                        }
                    }

                  /* scale if necessary */
                  if (scale != 1.0)
                    {
                      gsl_vector_view wv;

                      wv = gsl_vector_subvector(w->work, 0, iu + 1);
                      gsl_blas_dscal(scale, &wv.vector);
                    }

                  gsl_vector_set(w->work, lu - 1, x11);
                  gsl_vector_set(w->work, lu, x21);

                  /* update right hand side */
                  if (lu > 1)
                    {
                      gsl_vector_view v1, v2;

                      v1 = gsl_matrix_subcolumn(T, lu - 1, 0, lu - 1);
                      v2 = gsl_vector_subvector(w->work, 0, lu - 1);
                      gsl_blas_daxpy(-x11, &v1.vector, &v2.vector);

                      v1 = gsl_matrix_subcolumn(T, lu, 0, lu - 1);
                      gsl_blas_daxpy(-x21, &v1.vector, &v2.vector);
                    }

                  --l;
                } /* if (complex_pair) */
            } /* for (l = i - 1; l >= 0; --l) */

          /*
           * At this point, w->work is an eigenvector of the
           * Schur form T. To get an eigenvector of the original
           * matrix, we multiply on the left by Z, the matrix of
           * Schur vectors
           */

          ecol = gsl_matrix_complex_column(evec, iu);
          y = gsl_matrix_column(Z, iu);

          if (iu > 0)
            {
              gsl_vector_view x;

              Zv = gsl_matrix_submatrix(Z, 0, 0, N, iu);

              x = gsl_vector_subvector(w->work, 0, iu);

              /* compute Z * w->work and store it in Z(:,iu) */
              gsl_blas_dgemv(CblasNoTrans,
                             1.0,
                             &Zv.matrix,
                             &x.vector,
                             gsl_vector_get(w->work, iu),
                             &y.vector);
            } /* if (iu > 0) */

          /* store eigenvector into evec */

          ev = gsl_vector_complex_real(&ecol.vector);
          ev2 = gsl_vector_complex_imag(&ecol.vector);

          scale = 0.0;
          for (ii = 0; ii < N; ++ii)
            {
              double a = gsl_vector_get(&y.vector, ii);

              /* store real part of eigenvector */
              gsl_vector_set(&ev.vector, ii, a);

              /* set imaginary part to 0 */
              gsl_vector_set(&ev2.vector, ii, 0.0);

              if (fabs(a) > scale)
                scale = fabs(a);
            }

          if (scale != 0.0)
            scale = 1.0 / scale;

          /* scale by magnitude of largest element */
          gsl_blas_dscal(scale, &ev.vector);
        } /* if (GSL_IMAG(lambda) == 0.0) */
      else
        {
          gsl_vector_complex_view bv, xv;
          size_t k;
          int l;
          gsl_complex lambda2;

          /* complex eigenvector */

          /*
           * Store the complex conjugate eigenvalues in the right
           * slots in eval
           */
          GSL_SET_REAL(&lambda2, GSL_REAL(lambda));
          GSL_SET_IMAG(&lambda2, -GSL_IMAG(lambda));
          gsl_vector_complex_set(eval, iu - 1, lambda);
          gsl_vector_complex_set(eval, iu, lambda2);

          /*
           * First solve:
           *
           * [ T(i:i+1,i:i+1) - lambda*I ] * X = 0
           */

          if (fabs(gsl_matrix_get(T, iu - 1, iu)) >=
              fabs(gsl_matrix_get(T, iu, iu - 1)))
            {
              gsl_vector_set(w->work, iu - 1, 1.0);
              gsl_vector_set(w->work2, iu,
                             lambda_im / gsl_matrix_get(T, iu - 1, iu));
            }
          else
            {
              gsl_vector_set(w->work, iu - 1,
                             -lambda_im / gsl_matrix_get(T, iu, iu - 1));
              gsl_vector_set(w->work2, iu, 1.0);
            }
          gsl_vector_set(w->work, iu, 0.0);
          gsl_vector_set(w->work2, iu - 1, 0.0);