DSPR2(3)

💖 DSPR2(3) 💖

okay bestie, buckle up — this is a LAPACK page (the library, version coded into the footer, we'll get there) and it's genuinely one of the cuter BLAS routines. it's a Fortran file, living its best life at /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/BLAS/SRC/dspr2.f, and honestly? she ate. ✨

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🌸 NAME 🌸

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/BLAS/SRC/dspr2.f — that's the whole name, yes the entire path, no we're not shortening it, she's iconic and her full legal name is on the birth certificate 💅

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🦋 SYNOPSIS 🦋

🎀 Functions/Subroutines 🎀

• subroutine DSPR2 (uplo, n, alpha, x, incx, y, incy, ap) — hi, this is DSPR2, she's a subroutine, she has eight (8) arguments and she's not sorry about it 🫶

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🌈 Function/Subroutine Documentation 🌈

⭐ DSPR2 ⭐

subroutine DSPR2 (character uplo, integer n, double precision alpha, double precision, dimension(*) x, integer incx, double precision, dimension(*) y, integer incy, double precision, dimension(*) ap)

yeah that's the full signature, all character / integer / double precision goodness, with dimension(*) on x, y and ap — like, she's flexible, she doesn't need to know how big they are, that's a you problem 💀

🔥 Purpose 🔥

okay so. DSPR2 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. that's it. that's the whole vibe. rank-2 update, symmetric, packed, no cap. 🧚

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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, like this:

• 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.

literally just tell her which triangle, she's not a mind reader (she is a mind reader, but still, help her out) 🙈

💜 N

N is INTEGER.

on entry, N specifies the order of the matrix A. N must be at least zero. so 0 is allowed, negative is not the move. ⭐

💜 ALPHA

ALPHA is DOUBLE PRECISION.

on entry, ALPHA specifies the scalar alpha. that's her whole job, she's literally just a scalar, main character energy honestly.

💜 X

X is DOUBLE PRECISION array, dimension at least

( 1 + ( n - 1 )*abs( INCX ) ).

before entry, the incremented array X must contain the n element vector x. bestie. the incremented one. we don't make the rules 🎀

💜 INCX

INCX is INTEGER.

on entry, INCX specifies the increment for the elements of X. INCX must not be zero. fr fr, zero is a whole undefined behaviour situation, don't do it 💅

💜 Y

Y is DOUBLE PRECISION array, dimension at least

( 1 + ( n - 1 )*abs( INCY ) ).

before entry, the incremented array Y must contain the n element vector y. same deal as X, just the other one 🦋

💜 INCY

INCY is INTEGER.

on entry, INCY specifies the increment for the elements of Y. INCY must not be zero. again: not zero. periodt. 🔥

💜 AP

AP is DOUBLE PRECISION 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.

⚠️ okay this is the important one: AP gets overwritten on exit. like, full glow-up, in place. if you needed the old numbers, that's on you, she told you 💀

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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.

1986!! she's been slaying since before most of us were born, that's legacy behaviour 👑

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📍 Definition 📍

Definition at line 141 of file dspr2.f.

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💫 Author 💫

Generated automatically by Doxygen for LAPACK from the source code. (not a human, not a girlie, just Doxygen doing its little auto-generation thing 🤖💅)

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and that's the page!! 🎀 one (1) tiny little sign-off: this is LAPACK Version 3.12.0, dated with the good old /home/abui...SRC/dspr2.f(3) in the corner — go forth and rank-2 update your symmetric packed matrices, bestie, i'm obsessed 💖✨🦋