/*
 *
 * Solves the linear system `transpose(U)*U*x=L*transpose(L)*x=b' where `U'
 * and `L' are nonsingular bidiagonal matrices. The diagonals of `U' and
 * `L', respectively, are stored in the vector `d', and any of the secondary
 * diagonals is stored in the vector `e'. On input, `b' is the RHS. On
 * output, `b' contains the solution `x'.
 *
 */

void
cholsoltridiag (unsigned int n, double *d, double *e, double *b)
{
  unsigned int i;

  if (n == 0) {
    return;
    }
  *(b + 0) /= *(d + 0);
  for (i = 1; i < n; i++) {
    *(b + i) = (*(b + i) - *(e + i - 1) * *(b + i - 1)) / *(d + i);
    }
  *(b + n - 1) /= *(d + n - 1);
  for (i = n - 1; i > 0; i--) {
    *(b + i - 1) = (*(b + i - 1) - *(e + i - 1) * *(b + i)) / *(d + i - 1);
    }
  return;
  }