# Accession Number:

## ADA065624

# Title:

## SRRIT - A FORTRAN Subroutine to Calculate the Dominant Invariant Subspaces of a Real Matrix.

# Descriptive Note:

## Technical rept,

# Corporate Author:

## MARYLAND UNIV COLLEGE PARK COMPUTER SCIENCE CENTER

# Personal Author(s):

# Report Date:

## 1978-11-01

# Pagination or Media Count:

## 53.0

# Abstract:

SRRIT is a FORTRAN program to calculate an approximate orthonormal basis for a dominant invariant subspace of a real matrix A. Specifically, given an integer m, SRRIT attempts to compute a matrix Q with m orthonormal columns and real quasi-triangular matrix T of order m such that the equation AQ QT is satisfied up to a tolerence specified by the user. The eigenvalues of T are approximations to the m largest eigenvalues of A, and the columns of Q span the invariant subspace corresponding to those eigenvalues. SRRIT references A only through a user provided subroutine to form the product AQ hence it is suitable for large sparse problems. Author

# Descriptors:

# Subject Categories:

- Theoretical Mathematics
- Computer Programming and Software