BLAS/SRC/ssyr2k.f(3)

📦
version 3.12.1 · 4 versions
, in arch rolling

💖 SSYR2K — BLAS/SRC/ssyr2k.f 💖

okay so bestie, this is a page straight out of the LAPACK Library Functions Manual, and it's honestly kind of iconic. It's a Level 3 BLAS routine, it does symmetric rank-2k updates, and yes we're gonna go through every single parameter together because that's what friends do 🫶

✨ SYNOPSIS ✨

Functions/Subroutines

  • subroutine ssyr2k (uplo, trans, n, k, alpha, a, lda, b, ldb, beta, c, ldc) — SSYR2K, the main character herself 👑

🌸 Function/Subroutine Documentation 🌸

the signature, verbatim, no notes 💅

subroutine ssyr2k (character uplo, character trans, integer n, integer k,
    real alpha, real, dimension(lda,*) a, integer lda, real,
    dimension(ldb,*) b, integer ldb, real beta, real, dimension(ldc,*) c,
    integer ldc)

SSYR2K

🎀 Purpose 🎀

so what does she actually do? SSYR2K performs one of the symmetric rank 2k operations, and here they are in all their glory:

C := alpha*A*B**T + alpha*B*A**T + beta*C,

or

C := alpha*A**T*B + alpha*B**T*A + beta*C,

where alpha and beta are scalars, C is an n by n symmetric matrix, and A and B are n by k matrices in the first case, and k by n matrices in the second case. that's it, that's the whole vibe 🌈

💜 Parameters 💜

  • UPLO — UPLO is CHARACTER*1. On entry, UPLO specifies whether the upper or lower triangular part of the array C is to be referenced, as follows:
    • UPLO = 'U' or 'u' → Only the upper triangular part of C is to be referenced.
    • UPLO = 'L' or 'l' → Only the lower triangular part of C is to be referenced.
  • TRANS — TRANS is CHARACTER*1. On entry, TRANS specifies the operation to be performed, as follows:
    • TRANS = 'N' or 'n' → C := alpha*A*B**T + alpha*B*A**T + beta*C.
    • TRANS = 'T' or 't' → C := alpha*A**T*B + alpha*B**T*A + beta*C.
    • TRANS = 'C' or 'c' → C := alpha*A**T*B + alpha*B**T*A + beta*C.
  • N — N is INTEGER. On entry, N specifies the order of the matrix C. N must be at least zero. yes bestie, at least zero, we don't do negative orders here 🙈
  • K — K is INTEGER. On entry with TRANS = 'N' or 'n', K specifies the number of columns of the matrices A and B, and on entry with TRANS = 'T' or 't' or 'C' or 'c', K specifies the number of rows of the matrices A and B. K must be at least zero.
  • ALPHA — ALPHA is REAL. On entry, ALPHA specifies the scalar alpha. that's her, the queen of scaling 💅
  • A — A is REAL array, dimension ( LDA, ka ), where ka is k when TRANS = 'N' or 'n', and is n otherwise. Before entry with TRANS = 'N' or 'n', the leading n by k part of the array A must contain the matrix A; otherwise the leading k by n part of the array A must contain the matrix A.
  • LDA — LDA is INTEGER. On entry, LDA specifies the first dimension of A as declared in the calling (sub) program. When TRANS = 'N' or 'n' then LDA must be at least max( 1, n ), otherwise LDA must be at least max( 1, k ).
  • B — B is REAL array, dimension ( LDB, kb ), where kb is k when TRANS = 'N' or 'n', and is n otherwise. Before entry with TRANS = 'N' or 'n', the leading n by k part of the array B must contain the matrix B; otherwise the leading k by n part of the array B must contain the matrix B. (she's a whole twin situation with A, we love consistency ✨)
  • LDB — LDB is INTEGER. On entry, LDB specifies the first dimension of B as declared in the calling (sub) program. When TRANS = 'N' or 'n' then LDB must be at least max( 1, n ), otherwise LDB must be at least max( 1, k ).
  • BETA — BETA is REAL. On entry, BETA specifies the scalar beta. the other queen of scaling 🎀
  • C — C is REAL array, dimension ( LDC, N ). Before entry with UPLO = 'U' or 'u', the leading n by n upper triangular part of the array C must contain the upper triangular part of the symmetric matrix, and the strictly lower triangular part of C is not referenced. On exit, the upper triangular part of the array C is overwritten by the upper triangular part of the updated matrix. Before entry with UPLO = 'L' or 'l', the leading n by n lower triangular part of the array C must contain the lower triangular part of the symmetric matrix, and the strictly upper triangular part of C is not referenced. On exit, the lower triangular part of the array C is overwritten by the lower triangular part of the updated matrix. 🦋
  • LDC — LDC is INTEGER. On entry, LDC specifies the first dimension of C as declared in the calling (sub) program. LDC must be at least max( 1, n ).

👑 Author 👑

  • Univ. of Tennessee
  • Univ. of California Berkeley
  • Univ. of Colorado Denver
  • NAG Ltd.

🔥 Further Details: 🔥

  • Level 3 Blas routine.
  • -- Written on 8-February-1989.
    • Jack Dongarra, Argonne National Laboratory.
    • Iain Duff, AERE Harwell.
    • Jeremy Du Croz, Numerical Algorithms Group Ltd.
    • Sven Hammarling, Numerical Algorithms Group Ltd.

like, 1989?? they were out here doing symmetric rank-2k updates before I was even a thought. legends, fr fr 🌟

📍 Definition at line 191 of file ssyr2k.f.

💫 Author 💫

Generated automatically by Doxygen for LAPACK from the source code.

ngl the whole thing is a vibe: two triangular halves, one C, and a beta that just sits there scaling whatever you hand her. respect 😭💜

okay bestie that's the whole page, no crumbs left — and for the record this beauty is from LAPACK, Version 3.12.0, filed under BLAS/SRC/ssyr2k.f(3). slay, eat, periodt 💅✨🎀

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