Visible to Intel only — GUID: GUID-E8C0854F-EB77-4AC0-8028-496177CDD617
Visible to Intel only — GUID: GUID-E8C0854F-EB77-4AC0-8028-496177CDD617
?syr2
Performs a rank-2 update of a symmetric matrix.
Syntax
call ssyr2(uplo, n, alpha, x, incx, y, incy, a, lda)
call dsyr2(uplo, n, alpha, x, incx, y, incy, a, lda)
call syr2(a, x, y [,uplo][,alpha])
Include Files
- mkl.fi, blas.f90
Description
The ?syr2 routines perform a matrix-vector operation defined as
A := alpha*x*y'+ alpha*y*x' + A,
where:
alpha is scalar,
x and y are n-element vectors,
A is an n-by-n symmetric matrix.
Input Parameters
- uplo
-
CHARACTER*1. Specifies whether the upper or lower triangular part of the array a is used.
If uplo = 'U' or 'u', then the upper triangular part of the array a is used.
If uplo = 'L' or 'l', then the low triangular part of the array a is used.
- n
-
INTEGER. Specifies the order of the matrix A. The value of n must be at least zero.
- alpha
-
REAL for ssyr2
DOUBLE PRECISION for dsyr2
Specifies the scalar alpha.
- x
-
REAL for ssyr2
DOUBLE PRECISION for dsyr2
Array, size at least (1 + (n - 1)*abs(incx)). Before entry, the incremented array x must contain the n-element vector x.
- incx
-
INTEGER. Specifies the increment for the elements of x.
The value of incx must not be zero.
- y
-
REAL for ssyr2
DOUBLE PRECISION for dsyr2
Array, size at least (1 + (n - 1)*abs(incy)). Before entry, the incremented array y must contain the n-element vector y.
- incy
-
INTEGER. Specifies the increment for the elements of y. The value of incy must not be zero.
- a
-
REAL for ssyr2
DOUBLE PRECISION for dsyr2
Array, size (lda, n).
Before entry with uplo = 'U' or 'u', the leading n-by-n upper triangular part of the array a must contain the upper triangular part of the symmetric matrix and the strictly lower triangular part of a is not referenced.
Before entry with uplo = 'L' or 'l', the leading n-by-n lower triangular part of the array a must contain the lower triangular part of the symmetric matrix and the strictly upper triangular part of a is not referenced.
- lda
-
INTEGER. Specifies the leading dimension of a as declared in the calling (sub)program. The value of lda must be at least max(1, n).
Output Parameters
- a
-
With uplo = 'U' or 'u', the upper triangular part of the array a is overwritten by the upper triangular part of the updated matrix.
With uplo = 'L' or 'l', the lower triangular part of the array a is overwritten by the lower triangular part of the updated matrix.
BLAS 95 Interface Notes
Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see BLAS 95 Interface Conventions.
Specific details for the routine syr2 interface are the following:
- a
-
Holds the matrix A of size (n,n).
- x
-
Holds the vector x of length n.
- y
-
Holds the vector y of length n.
- uplo
-
Must be 'U' or 'L'. The default value is 'U'.
- alpha
-
The default value is 1.