ssytrf - compute the factorization of a real symmetric matrix A using the Bunch-Kaufman diagonal pivoting method
SUBROUTINE SSYTRF(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER*1 UPLO INTEGER N, LDA, LDWORK, INFO INTEGER IPIVOT(*) REAL A(LDA,*), WORK(*) SUBROUTINE SSYTRF_64(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER*1 UPLO INTEGER*8 N, LDA, LDWORK, INFO INTEGER*8 IPIVOT(*) REAL A(LDA,*), WORK(*) F95 INTERFACE SUBROUTINE SYTRF(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER(LEN=1) :: UPLO INTEGER :: N, LDA, LDWORK, INFO INTEGER, DIMENSION(:) :: IPIVOT REAL, DIMENSION(:) :: WORK REAL, DIMENSION(:,:) :: A SUBROUTINE SYTRF_64(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER(LEN=1) :: UPLO INTEGER(8) :: N, LDA, LDWORK, INFO INTEGER(8), DIMENSION(:) :: IPIVOT REAL, DIMENSION(:) :: WORK REAL, DIMENSION(:,:) :: A C INTERFACE #include <sunperf.h> void ssytrf(char uplo, int n, float *a, int lda, int *ipivot, int *info); void ssytrf_64(char uplo, long n, float *a, long lda, long *ipivot, long *info);
Oracle Solaris Studio Performance Library ssytrf(3P) NAME ssytrf - compute the factorization of a real symmetric matrix A using the Bunch-Kaufman diagonal pivoting method SYNOPSIS SUBROUTINE SSYTRF(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER*1 UPLO INTEGER N, LDA, LDWORK, INFO INTEGER IPIVOT(*) REAL A(LDA,*), WORK(*) SUBROUTINE SSYTRF_64(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER*1 UPLO INTEGER*8 N, LDA, LDWORK, INFO INTEGER*8 IPIVOT(*) REAL A(LDA,*), WORK(*) F95 INTERFACE SUBROUTINE SYTRF(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER(LEN=1) :: UPLO INTEGER :: N, LDA, LDWORK, INFO INTEGER, DIMENSION(:) :: IPIVOT REAL, DIMENSION(:) :: WORK REAL, DIMENSION(:,:) :: A SUBROUTINE SYTRF_64(UPLO, N, A, LDA, IPIVOT, WORK, LDWORK, INFO) CHARACTER(LEN=1) :: UPLO INTEGER(8) :: N, LDA, LDWORK, INFO INTEGER(8), DIMENSION(:) :: IPIVOT REAL, DIMENSION(:) :: WORK REAL, DIMENSION(:,:) :: A C INTERFACE #include <sunperf.h> void ssytrf(char uplo, int n, float *a, int lda, int *ipivot, int *info); void ssytrf_64(char uplo, long n, float *a, long lda, long *ipivot, long *info); PURPOSE ssytrf computes the factorization of a real symmetric matrix A using the Bunch-Kaufman diagonal pivoting method. The form of the factoriza- tion is A = U*D*U**T or A = L*D*L**T where U (or L) is a product of permutation and unit upper (lower) tri- angular matrices, and D is symmetric and block diagonal with 1-by-1 and 2-by-2 diagonal blocks. This is the blocked version of the algorithm, calling Level 3 BLAS. ARGUMENTS UPLO (input) = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored. N (input) The order of the matrix A. N >= 0. A (input/output) On entry, the symmetric matrix A. If UPLO = 'U', the leading N-by-N upper triangular part of A contains the upper triangu- lar part of the matrix A, and the strictly lower triangular part of A is not referenced. If UPLO = 'L', the leading N- by-N lower triangular part of A contains the lower triangular part of the matrix A, and the strictly upper triangular part of A is not referenced. On exit, the block diagonal matrix D and the multipliers used to obtain the factor U or L (see below for further details). LDA (input) The leading dimension of the array A. LDA >= max(1,N). IPIVOT (output) Details of the interchanges and the block structure of D. If IPIVOT(k) > 0, then rows and columns k and IPIVOT(k) were interchanged and D(k,k) is a 1-by-1 diagonal block. If UPLO = 'U' and IPIVOT(k) = IPIVOT(k-1) < 0, then rows and columns k-1 and -IPIVOT(k) were interchanged and D(k-1:k,k-1:k) is a 2-by-2 diagonal block. If UPLO = 'L' and IPIVOT(k) = IPIVOT(k+1) < 0, then rows and columns k+1 and -IPIVOT(k) were interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block. WORK (workspace) On exit, if INFO = 0, WORK(1) returns the optimal LDWORK. LDWORK (input) The length of WORK. LDWORK >=1. For best performance LDWORK >= N*NB, where NB is the block size returned by ILAENV. If LDWORK = -1, then a workspace query is assumed; the rou- tine only calculates the optimal size of the WORK array, returns this value as the first entry of the WORK array, and no error message related to LDWORK is issued by XERBLA. INFO (output) = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value > 0: if INFO = i, D(i,i) is exactly zero. The factorization has been completed, but the block diagonal matrix D is exactly singular, and division by zero will occur if it is used to solve a system of equations. FURTHER DETAILS If UPLO = 'U', then A = U*D*U', where U = P(n)*U(n)* ... *P(k)U(k)* ..., i.e., U is a product of terms P(k)*U(k), where k decreases from n to 1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1 and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as defined by IPIVOT(k), and U(k) is a unit upper triangular matrix, such that if the diagonal block D(k) is of order s (s = 1 or 2), then ( I v 0 ) k-s U(k) = ( 0 I 0 ) s ( 0 0 I ) n-k k-s s n-k If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k). If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k), and A(k,k), and v overwrites A(1:k-2,k-1:k). If UPLO = 'L', then A = L*D*L', where L = P(1)*L(1)* ... *P(k)*L(k)* ..., i.e., L is a product of terms P(k)*L(k), where k increases from 1 to n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1 and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as defined by IPIVOT(k), and L(k) is a unit lower triangular matrix, such that if the diagonal block D(k) is of order s (s = 1 or 2), then ( I 0 0 ) k-1 L(k) = ( 0 I 0 ) s ( 0 v I ) n-k-s+1 k-1 s n-k-s+1 If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k). If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k), and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1). 7 Nov 2015 ssytrf(3P)