© 1981 by British Computer Society
The determination of eigenvalues of symmetric quindiagonal matrices

1 Department of Computer Science, The City University, Northampton Square, London, UK, 2 School of Mathematics and Computing, Slough College of Higher Education, Wellington Street, Slough, UK
Evans (1975) has described a method for finding the eigenvalues of quindiagonal matrices A based on the bisection and the Sturm sequence property of the leading principal minors Pi(
) of A
I. The algorithms there presented contained certain typographical errors, but even with these removed the procedures give incorrect results for certain matrices which have some zero Pi(
) at the point of bisection. This paper describes a modification, based on earlier work on general band matrices, in which the sign of Pi(
) is determined without calculating its value. Thus there are no problems with underflow or overflow.
Received April 1980.
* Department of Computer Science, The City University, Northampton Square, London EC1V 0HB.
School of Mathematics and Computing, Slough College of Higher Education, Wellington Street, Slough, Berkshire SL1 1YG.