BLAS/SRC/sspr2.f(3)

💖 BLAS/SRC/sspr2.f 💖

okay bestie, so this is the manual page for BLAS/SRC/sspr2.f — a little Fortran file living in the BLAS source tree (that's the Basic Linear Algebra Subprograms, the bedrock of like... every numerical thing ever, iykyk). It's a Level 2 BLAS routine and it's here to do one very specific, very slay job. Let's get into it 🫶

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine sspr2 (uplo, n, alpha, x, incx, y, incy, ap)

SSPR2

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🌸 Function/Subroutine Documentation 🌸

subroutine sspr2 (character uplo, integer n, real alpha, real, dimension(*) x, integer incx, real, dimension(*) y, integer incy, real, dimension(*) ap)

SSPR2

🎀 Purpose 🎀

okay so here's the whole vibe: SSPR2 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, supplied in packed form.

like. it's giving "two outer products, one scalar, and A gets updated in place". iconic behavior honestly 💅

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👑 Parameters 👑

• UPLO — UPLO is CHARACTER*1. On entry, UPLO specifies whether the upper or lower triangular part of the matrix A is supplied in the packed array AP as follows:
  • UPLO = 'U' or 'u' — The upper triangular part of A is supplied in AP.
  • UPLO = 'L' or 'l' — The lower triangular part of A is supplied in AP.
• N — N is INTEGER. On entry, N specifies the order of the matrix A. N must be at least zero.
• ALPHA — ALPHA is REAL. On entry, ALPHA specifies the scalar alpha.
• 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.

🚨 bestie. INCX must not be zero. no cap. that's a hard no.

• 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 as INCX — zero is NOT the move here 💀

• AP — AP is REAL array, dimension at least ( ( n*( n + 1 ) )/2 ). Before entry with UPLO = 'U' or 'u', the array AP must contain the upper triangular part of the symmetric matrix packed sequentially, column by column, so that AP( 1 ) contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 ) and a( 2, 2 ) respectively, and so on. On exit, the array AP is overwritten by the upper triangular part of the updated matrix.

Before entry with UPLO = 'L' or 'l', the array AP must contain the lower triangular part of the symmetric matrix packed sequentially, column by column, so that AP( 1 ) contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 ) and a( 3, 1 ) respectively, and so on. On exit, the array AP is overwritten by the lower triangular part of the updated matrix.

✨ psst — AP gets overwritten on exit. it's an in-place glow-up, not a copy situation. pack accordingly 🦋

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💜 Author 💜

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

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🔥 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.

Definition at line 141 of file sspr2.f.

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⭐ Author ⭐

Generated automatically by Doxygen for LAPACK from the source code.

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and that's the whole page, bestie!! no notes, every single flag accounted for, we ate and left zero crumbs 🍓✨

this lil legend was brought to you by Version 3.12.0, dated Tue Nov 28 2023 12:08:41, straight out of BLAS/SRC/sspr2.f(3). go forth and pack your symmetric matrices correctly, ily 💖🌈