BLAS/SRC/ssyr2.f(3)

💖 NAME 💖

okay bestie, so this is BLAS/SRC/ssyr2.f — a lil page from the LAPACK manual (yes, that LAPACK, the linear algebra icon 👑) and it's all about one very specific little Fortran subroutine. no cap, it does exactly one thing and it does it gorgeously. ✨

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🌸 SYNOPSIS 🌸

✨ Functions/Subroutines ✨

• subroutine ssyr2 (uplo, n, alpha, x, incx, y, incy, a, lda) — SSYR2 🫶

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🦋 Function/Subroutine Documentation 🦋

subroutine ssyr2 (character uplo, integer n, real alpha, real, dimension(*)
    x, integer incx, real, dimension(*) y, integer incy, real,
    dimension(lda,*) a, integer lda)

SSYR2 💅

🎀 Purpose 🎀

okay so here's the whole vibe: SSYR2 performs the symmetric rank 2 operation

   A := alpha*x*y**T + alpha*y*x**T + A,

where alpha is a scalar, x and y are n element vectors and A is an n by n symmetric matrix. literally that's it, that's the whole job, and it ate. 💖

🍓 Parameters 🍓

• UPLO — UPLO is CHARACTER*1. on entry, UPLO specifies whether the upper or lower triangular part of the array A is to be referenced, as follows:

   UPLO = 'U' or 'u'   Only the upper triangular part of A
                       is to be referenced.

   UPLO = 'L' or 'l'   Only the lower triangular part of A
                       is to be referenced.

• N — N is INTEGER. on entry, N specifies the order of the matrix A. N must be at least zero. (zero is allowed bestie, it's giving "empty but valid" 💀✨)
• ALPHA — ALPHA is REAL. on entry, ALPHA specifies the scalar alpha. it's the lil multiplier, the main character of the arithmetic 👑
• X — X is REAL array, dimension at least ( 1 + ( n - 1 )*abs( INCX ) ). before entry, the incremented array X must contain the n element vector x. 🦋
• INCX — INCX is INTEGER. on entry, INCX specifies the increment for the elements of X. INCX must not be zero. fr fr, zero is not the move.
• Y — Y is REAL array, dimension at least ( 1 + ( n - 1 )*abs( INCY ) ). before entry, the incremented array Y must contain the n element vector y. 🌈
• INCY — INCY is INTEGER. on entry, INCY specifies the increment for the elements of Y. INCY must not be zero. same energy, don't do it.
• A — A is REAL array, dimension ( 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. on exit, the upper triangular part of the array A 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 A must contain the lower triangular part of the symmetric matrix and the strictly upper triangular part of A is not referenced. on exit, the lower triangular part of the array A is overwritten by the lower triangular part of the updated matrix. 💅 (tl;dr: the half you told it about gets updated in place, the other half is simply not invited to the party 🙈)
• LDA — LDA is INTEGER. on entry, LDA specifies the first dimension of A as declared in the calling (sub) program. LDA must be at least max( 1, n ). periodt.

💜 Author 💜

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

(an absolute dream team, no notes 🫶)

⭐ Further Details ⭐

Level 2 Blas routine.

-- Written on 22-October-1986.
   Jack Dongarra, Argonne National Lab.
   Jeremy Du Croz, Nag Central Office.
   Sven Hammarling, Nag Central Office.
   Richard Hanson, Sandia National Labs.

like, 1986?? the longevity, the legacy, the iconic behaviour 😭💖

Definition at line 146 of file ssyr2.f.

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🌟 Author 🌟

Generated automatically by Doxygen for LAPACK from the source code. (not me writing this by hand, the robots did it, and honestly? slay 🤖✨)

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okay that's the whole page bestie!! this was Version 3.12.0, dated Tue Nov 28 2023 12:08:41, from BLAS/SRC/ssyr2.f(3) — go forth and rank-2-update your symmetric matrices responsibly, mwah 💋🎀🦋