DGEMV(3)

DGEMV(3) 💅✨

okay so this page is from /home/abui...SRC/dgemv.f(3), straight out of the Library Functions Manual — and bestie, it is so much more fun than it looks, i promise 🫶

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✨ NAME ✨

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/BLAS/SRC/dgemv.f

like yes that's literally a whole path as the name, she's got main character energy and a very long address, we respect it 💀

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🦋 SYNOPSIS 🦋

Functions/Subroutines

subroutine DGEMV (trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

that's the short version — DGEMV, lowercase vibes only, arguments all lined up 🎀

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🌸 Function/Subroutine Documentation 🌸

subroutine DGEMV (character trans, integer m, integer n, double precision
    alpha, double precision, dimension(lda,*) a, integer lda, double
    precision, dimension(*) x, integer incx, double precision beta, double
    precision, dimension(*) y, integer incy)

DGEMV 🫶 (the full-length version, same girl, more detail)

Purpose

!> !> DGEMV performs one of the matrix-vector operations !> !> y := alpha*A*x + beta*y, or y := alpha*A**T*x + beta*y, !> !> where alpha and beta are scalars, x and y are vectors and A is an !> m by n matrix. !>

so literally: you got a matrix A, you got vectors x and y, you got scalars alpha and beta, and DGEMV does the whole multiply-and-add situation for you. either the normal way or the transposed way, and honestly? iconic 🔥

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🎀 Parameters 🎀

• TRANS — TRANS is CHARACTER*1. On entry, TRANS specifies the operation to be performed as follows:
  • TRANS = 'N' or 'n' → y := alpha*A*x + beta*y.
  • TRANS = 'T' or 't' → y := alpha*A**T*x + beta*y.
  • TRANS = 'C' or 'c' → y := alpha*A**T*x + beta*y.

ngl the 'T' and 'C' cases are doing the exact same thing here, that's just how she is 💅

• M — M is INTEGER. On entry, M specifies the number of rows of the matrix A. M must be at least zero. (zero is allowed, she just vibes and leaves early ✨)
• N — N is INTEGER. On entry, N specifies the number of columns of the matrix A. N must be at least zero.
• ALPHA — ALPHA is DOUBLE PRECISION. On entry, ALPHA specifies the scalar alpha. that's the little multiplier bestie 🌸
• A — A is DOUBLE PRECISION array, dimension ( LDA, N ). Before entry, the leading m by n part of the array A must contain the matrix of coefficients. 👑
• 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, m ). don't skimp on it, fr fr 🫶
• X — X is DOUBLE PRECISION array, dimension at least ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n' and at least ( 1 + ( m - 1 )*abs( INCX ) ) otherwise. Before entry, the incremented array X must contain the vector x. mind the n vs m swap depending on TRANS, iykyk 💀
• INCX — INCX is INTEGER. On entry, INCX specifies the increment for the elements of X. INCX must not be zero. seriously, not zero, that's a hard no 🙈
• BETA — BETA is DOUBLE PRECISION. On entry, BETA specifies the scalar beta. When BETA is supplied as zero then Y need not be set on input. cute little shortcut, love that for you ✨
• Y — Y is DOUBLE PRECISION array, dimension at least ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n' and at least ( 1 + ( n - 1 )*abs( INCY ) ) otherwise. Before entry with BETA non-zero, the incremented array Y must contain the vector y. On exit, Y is overwritten by the updated vector y. If either m or n is zero, then Y not referenced and the function performs a quick return. okay so she literally does not touch Y in that case, she's out the door 🏃‍♀️💨
• INCY — INCY is INTEGER. On entry, INCY specifies the increment for the elements of Y. INCY must not be zero. same rule as INCX, no zeros allowed periodt 💅

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👑 Author 👑

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

the whole squad showed up for this one 🫶🌈

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Further Details

!> !> Level 2 Blas routine. !> The vector and matrix arguments are not referenced when N = 0, or M = 0 !> !> -- 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. !>

okay 1986!! she's been serving since before most of us were born, that's legacy behavior 👑 and for real, if N = 0 or M = 0 the vector and matrix arguments are not referenced — she's not even looking at them 💀

Definition at line 157 of file dgemv.f. 📍

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⭐ Author ⭐

Generated automatically by Doxygen for LAPACK from the source code. not a human, a little robot did this, and it ate 🤖✨

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btw quick vibe check: INCX and INCY must not be zero, LDA must be at least max( 1, m ), M and N must be at least zero, and Y gets overwritten on exit unless m or n is zero. no cap, those are the rules 🫶

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alright bestie that's the whole page!! 🎀 this was LAPACK, Version 3.12.0, and our girl lives at /home/abui...SRC/dgemv.f(3) — go forth and multiply those matrices, slay 💖✨🦋