SRC/dopmtr.f(3)

💅 NAME 💅

SRC/dopmtr.f — okay so this is the SRC/dopmtr.f(3) page from the Library Functions Manual, and it’s here to explain the dopmtr subroutine. Periodt. 💖

✨ SYNOPSIS ✨

🦋 Functions/Subroutines 🦋

• subroutine dopmtr (side, uplo, trans, m, n, ap, tau, c, ldc, work, info) — DOPMTR

🌸 Function/Subroutine Documentation 🌸

subroutine dopmtr (character side, character uplo, character trans, integer
    m, integer n, double precision, dimension( * ) ap, double precision,
    dimension( * ) tau, double precision, dimension( ldc, * ) c, integer
    ldc, double precision, dimension( * ) work, integer info)

DOPMTR

🌈 Purpose 🌈

Okay bestie, here’s the tea: DOPMTR overwrites the general real M-by-N matrix C with

                SIDE = 'L'     SIDE = 'R'
TRANS = 'N':      Q * C          C * Q
TRANS = 'T':      Q**T * C       C * Q**T

where Q is a real orthogonal matrix of order nq, with nq = m if SIDE = 'L' and nq = n if SIDE = 'R'. Q is defined as the product of nq-1 elementary reflectors, as returned by DSPTRD using packed storage:

if UPLO = 'U', Q = H(nq-1) . . . H(2) H(1);

if UPLO = 'L', Q = H(1) H(2) . . . H(nq-1).

🎀 Parameters 🎀

• SIDE — so like, SIDE is CHARACTER*1, and it tells us which side to apply Q or QT from: = 'L': apply Q or QT from the Left; = 'R': apply Q or Q**T from the Right. Left/right main character energy, iykyk. 💅
• UPLO — UPLO is CHARACTER*1: = 'U': Upper triangular packed storage used in previous call to DSPTRD; = 'L': Lower triangular packed storage used in previous call to DSPTRD. It’s giving “which packed-storage era are we continuing?” ✨
• TRANS — TRANS is CHARACTER*1: = 'N': No transpose, apply Q; = 'T': Transpose, apply Q**T. No transpose? Transpose? the drama of it all.
• M — M is INTEGER, and it’s the number of rows of the matrix C. M >= 0. No negative-row nonsense, bestie. 🫶
• N — N is INTEGER, the number of columns of the matrix C. N >= 0. Respect the column count, fr fr.
• AP — AP is DOUBLE PRECISION array, dimension (M*(M+1)/2) if SIDE = 'L', (N*(N+1)/2) if SIDE = 'R'. These are the vectors which define the elementary reflectors, as returned by DSPTRD. Heads up: AP is modified by the routine but restored on exit. Iconic behavior, honestly. 🌈
• TAU — TAU is DOUBLE PRECISION array, dimension (M-1) if SIDE = 'L' or (N-1) if SIDE = 'R'. TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by DSPTRD. 🍓
• C — C is DOUBLE PRECISION array, dimension (LDC,N). On entry, the M-by-N matrix C. On exit, C is overwritten by Q*C or Q**T*C or C*Q**T or C*Q. So yeah, C gets a full glow-up, not a gentle edit. 💀
• LDC — LDC is INTEGER, the leading dimension of the array C. LDC >= max(1,M). Respect the leading dimension, no cap. 👑
• WORK — WORK is DOUBLE PRECISION array, dimension (N) if SIDE = 'L', (M) if SIDE = 'R'. 🧚
• INFO — INFO is INTEGER: = 0: successful exit; < 0: if INFO = -i, the i-th argument had an illegal value. So if INFO is negative, it’s not a vibe — check that i-th argument. 🚨

👑 Author 👑

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 148 of file dopmtr.f.

🧚 Author 🧚

Generated automatically by Doxygen for LAPACK from the source code.

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💖 And that’s the whole page, bestie — LAPACK Version 3.12.0, source SRC/dopmtr.f(3). The footer didn’t give a date, so no made-up date from me; consider this sign-off stamped with pure 3.12.0 sparkle. 🫶✨