HP MLIB User's Guide Vol. 2 7th Ed.

Chapter 9 LAPACK Auxiliary Subprograms 663
Compute norm of general tridiagonal matrix SLANGT/DLANGT/CLANGT/ZLANGT
Name SLANGT/DLANGT/CLANGT/ZLANGT
Compute norm of general tridiagonal matrix
Purpose These subprograms compute a norm of a general tridiagonal matrix A. A
matrix A = (a
ij
) is tridiagonal if its nonzero elements lie only on the principal
diagonal (i = j), the subdiagonal (i = j+1), and the superdiagonal (i = j−1) of
the matrix.
Matrix
Storage
The following example illustrates the storage of general tridiagonal matrices.
Consider the following tridiagonal matrix of order n =7:
The subdiagonal is stored in array dl, the principal diagonal is stored in array
d, and the superdiagonal is stored in array du, as follows:
Usage LAPACK:
CHARACTER*1 norm
INTEGER*4 n
REAL*4 d(n), dl(n−1), du(n−1)
REAL*4 anorm, SLANGT
anorm = SLANGT(norm, n, dl, d, du)
111200000
2122230000
0323334 0 0 0
0 0 43 44 45 0 0
0 0 0 54 55 56 0
0 0 0 0656667
000007677
i dl(i) d(i) du(i)
12111 12
23222 23
34333 34
45444 45
56555 56
67666 67
777