NAG Library Chapter Introduction
Scope of the Chapter
This chapter is concerned with the calculation of determinants of square matrices.
Background to the Problems
The routines in this chapter compute the determinant of a square matrix
. The matrix is assumed to have first been decomposed into triangular factors
using routines from Chapter F07
If is positive definite, then , and the determinant is the product of the squares of the diagonal elements of . Otherwise, the routines in this chapter use the Dolittle form of the decomposition, where has unit elements on its diagonal. The determinant is then the product of the diagonal elements of , taking account of possible sign changes due to row interchanges.
To avoid overflow or underflow in the computation of the determinant, some scaling is associated with each multiplication in the product of the relevant diagonal elements. The final value is represented by
is an integer and
For complex valued determinants the real and imaginary parts are scaled separately.
Recommendations on Choice and Use of Available Routines
It is extremely wasteful of computer time and storage to use an inappropriate routine, for example to use a routine requiring a complex matrix when is real. Most programmers will know whether their matrix is real or complex, but may be less certain whether or not a real symmetric matrix is positive definite, i.e., all eigenvalues of . A real symmetric matrix not known to be positive definite must be treated as a general real matrix.
In all other cases either the band routine or the general routines must be used.
The routines in this chapter are general purpose routines. These give the value of the determinant in its scaled form,
, given the triangular decomposition of the matrix from a suitable routine from Chapter F07
|Determinants of factorized matrices,|| |
| real symmetric band positive definite matrix|| ||f03bhf|
| real symmetric positive definite matrix|| ||f03bff|
Auxiliary Routines Associated with Library Routine Arguments
Routines Withdrawn or Scheduled for Withdrawal
The following lists all those routines that have been withdrawn since Mark 19 of the Library or are scheduled for withdrawal at one of the next two marks.
Fox L (1964) An Introduction to Numerical Linear Algebra Oxford University Press
Wilkinson J H and Reinsch C (1971) Handbook for Automatic Computation II, Linear Algebra Springer–Verlag