HP MLIB User's Guide Vol. 1 7th Ed.

Chapter 3 Basic Matrix Operations 287

Rank-2k update SSYR2K/DSYR2K/CHER2K/CSYR2K/ZHER2K/ZSYR2K

k Number of rows or columns in matrices A and B,

depending on trans; refer to the description of a for

details. k ≥ 0; if k = 0, the subprograms do not reference

a or b.

alpha The scalar α. If alpha = 0, the subprograms compute

C ←βC without referencing a or b.

a Array containing the matrix A, whose size is indicated

by trans:

’N’ or ’n’ A is n-by-k

otherwise A is k-by-n

lda The leading dimension of array a as declared in the

calling program unit, with lda ≥ max (the number of

rows of A,1).

b Array containing matrix B, which is the same size as

matrix A. Refer to the description of a for details.

ldb The leading dimension of array b as declared in the

calling program unit, with ldb ≥ max (the number of

rows of B,1).

beta The scalar β.

c Array whose upper or lower triangle, as speciﬁed by

uplo, contains the upper or lower triangle of the n-by-n

symmetric or Hermitian matrix C. Not used as input if

beta = 0.

ldc The leading dimension of array c as declared in the

calling program unit, with ldc ≥ max(n,1).

Output c The upper or lower triangle of the updated matrix C, as

speciﬁed by uplo, replaces the upper or lower triangle

of the input, respectively. The other triangle of c is

unchanged.

Notes These subprograms conform to speciﬁcations of the Level 3 BLAS.

If an error in the arguments is detected, the subprograms call error handler

XERBLA, which writes an error message onto the standard error ﬁle and

terminates execution. The standard version of XERBLA (refer to the end of this

chapter) can be replaced with a user-supplied version to change the error

procedure.