DLAQP2(3)

💅 DLAQP2(3) — Library Functions Manual 💅

okay so bestie, welcome to the DLAQP2(3) page from the Library Functions Manual. This one is a LAPACK subroutine and it's giving QR-with-column-pivoting energy. The NAME line is literally this file path: /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dlaqp2.f. Periodt. 💖

---

✨ SYNOPSIS ✨

🌈 Functions/Subroutines 🌈

• subroutine DLAQP2 (m, n, offset, a, lda, jpvt, tau, vn1, vn2, work) — DLAQP2 computes a QR factorization with column pivoting of the matrix block. No cap, that's the whole vibe. 🦋

---

🦋 Function/Subroutine Documentation 🦋

   subroutine DLAQP2 (integer m, integer n, integer offset, double precision,
       dimension( lda, * ) a, integer lda, integer, dimension( * ) jpvt, double
       precision, dimension( * ) tau, double precision, dimension( * ) vn1,
       double precision, dimension( * ) vn2, double precision, dimension( * )
       work)

DLAQP2 computes a QR factorization with column pivoting of the matrix block. Slay. ✨

🎯 Purpose 🎯

okay so the actual purpose is this: DLAQP2 computes a QR factorization with column pivoting of the block A(OFFSET+1:M,1:N). The block A(1:OFFSET,1:N) is accordingly pivoted, but not factorized. That's the tea. ☕

🧚 Parameters 🧚

• M — INTEGER. The number of rows of the matrix A. M >= 0.
• N — INTEGER. The number of columns of the matrix A. N >= 0.
• OFFSET — INTEGER. The number of rows of the matrix A that must be pivoted but not factorized. OFFSET >= 0.
• A — DOUBLE PRECISION array, dimension (LDA,N). On entry, the M-by-N matrix A. On exit, the upper triangle of block A(OFFSET+1:M,1:N) is the triangular factor obtained; the elements in block A(OFFSET+1:M,1:N) below the diagonal, together with the array TAU, represent the orthogonal matrix Q as a product of elementary reflectors. Block A(1:OFFSET,1:N) has been accordingly pivoted, but not factorized. 💅
• LDA — INTEGER. The leading dimension of the array A. LDA >= max(1,M).
• JPVT — INTEGER array, dimension (N). On entry, if JPVT(i) .ne. 0, the i-th column of A is permuted to the front of A*P (a leading column); if JPVT(i) = 0, the i-th column of A is a free column. On exit, if JPVT(i) = k, then the i-th column of A*P was the k-th column of A. 🫶
• TAU — DOUBLE PRECISION array, dimension (min(M,N)). The scalar factors of the elementary reflectors.
• VN1 — DOUBLE PRECISION array, dimension (N). The vector with the partial column norms.
• VN2 — DOUBLE PRECISION array, dimension (N). The vector with the exact column norms.
• WORK — DOUBLE PRECISION array, dimension (N). That's it, that's the whole description. 😭

👑 Author 👑

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

💖 Contributors: 💖

• G. Quintana-Orti, Depto. de Informatica, Universidad Jaime I, Spain
• X. Sun, Computer Science Dept., Duke University, USA
• Partial column norm updating strategy modified on April 2011 Z. Drmac and Z. Bujanovic, Dept. of Mathematics, University of Zagreb, Croatia.

📚 References: 📚

LAPACK Working Note 176. Iconic. 🌈

📍 Definition at line 147 of file dlaqp2.f

Definition at line 147 of file dlaqp2.f.

---

🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code. 🎀

---

💖 Cute sign-off: this is LAPACK Version 3.12.0, sourced from /home/abui...RC/dlaqp2.f(3) — the footer doesn't print a date, so no cap on the vibe. Bye bestie! 🫶💜