HPL_dger(3)

💖 HPL_dger — the glow-up your matrix deserves 💖

okay bestie, so this one is a function from the HPL Library Functions manual, and it's called HPL_dger. It's a rank 1 update and it's lowkey iconic. Let's get into it. 🫶

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✨ NAME ✨

HPL_dger — literally just: A := alpha * x * y^T + A. that's the whole vibe. 💅

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🌸 SYNOPSIS 🌸

#include "hpl.h"

void HPL_dger( const enum HPL_ORDER ORDER, const int M, const int N,
const double ALPHA, const double * X, const int INCX, double * Y, const
int INCY, double * A, const int LDA );

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🦋 DESCRIPTION 🦋

so HPL_dger performs the rank 1 operation

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

where alpha is a scalar, x is an m-element vector, y is an n-element vector and A is an m by n matrix. no cap, that's it. that's the whole function. main character energy fr fr. 👑

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🎀 ARGUMENTS 🎀

okay now the part everyone skips but should NOT skip, because every single one of these matters:

• ORDER — (local input) const enum HPL_ORDER — on entry, ORDER specifies the storage format of the operands, and it goes like this:
  • ORDER = HplRowMajor
  • ORDER = HplColumnMajor

pick one, bestie. it's giving "choose your fighter". 🌈

• M — (local input) const int — on entry, M specifies the number of rows of the matrix A. M must be at least zero. (yes, zero is allowed. no negativity here. ✋)
• N — (local input) const int — on entry, N specifies the number of columns of the matrix A. N must be at least zero. same rules, keep it non-negative.
• ALPHA — (local input) const double — on entry, ALPHA specifies the scalar alpha. 🍓 and here's the tea: when ALPHA is supplied as zero, then X and Y need not be set on input. free pass, we love to see it.
• X — (local input) const double * — on entry, X is an incremented array of dimension at least ( 1 + ( m - 1 ) * abs( INCX ) ) that contains the vector x. ⭐
• INCX — (local input) const int — on entry, INCX specifies the increment for the elements of X. 🚨 INCX must not be zero. do not. i'm serious.
• Y — (local input) double * — on entry, Y is an incremented array of dimension at least ( 1 + ( n - 1 ) * abs( INCY ) ) that contains the vector y. ✨
• INCY — (local input) const int — 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.
• A — (local input/output) double * — on entry, A points to an array of size equal to or greater than LDA * n. before entry, the leading m by n part of the array A must contain the matrix coefficients. on exit, A is overwritten by the updated matrix. so yeah she's getting a whole new look, hope you didn't need the old one. 💀
• LDA — (local input) const int — on entry, LDA specifies the leading dimension of A as declared in the calling (sub) program. LDA must be at least MAX(1,m). remember it. write it down. MAX(1,m). 🧚

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🔥 EXAMPLE 🔥

here's the example, copy-paste it exactly as it is, i'm not touching a single character:

#include "hpl.h"

int main(int argc, char *argv[])
{
   double a[2*2], x[2], y[2];
   a[0] = 1.0; a[1] = 2.0; a[2] = 3.0; a[3] = 3.0;
   x[0] = 2.0; x[1] = 1.0; y[2] = 1.0; y[3] = 2.0;
   HPL_dger( HplColumnMajor, 2, 2, 2.0, x, 1, y, 1,
             a, 2 );
   printf("y=[%f,%f]\n", y[0], y[1]);
   exit(0); return(0);
}

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👑 SEE ALSO 👑

go read these next, they're the friend group:

• HPL_dgemv (3)
• HPL_dtrsv (3)

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💖 quick vibe check before you go: INCX and INCY cannot be zero, M and N must be at least zero, and LDA must be at least MAX(1,m). the function will not be nice about it. protect your arrays. 🫶

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and that's the whole page, bestie!! 🌈✨ this was written for HPL 2.2, dated February 24, 2016 — yeah it's a lil vintage but she still ate. mwah. 💅💖🎀🦋