DLACN2(3)

💅 DLACN2(3) — Library Functions Manual

okay so bestie, welcome to the DLACN2(3) page from the Library Functions Manual 💖. This is the whole glow-up of the dlacn2.f(3) page, and we're folding the manual-name situation in right here instead of copying that header line. We're about to make reverse communication for 1-norm estimation make sense. ✨

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🌸 NAME

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dlacn2.f

That's the name/path, no cap. 🫶

✨ SYNOPSIS

🧚 Functions/Subroutines

subroutine DLACN2 (n, v, x, isgn, est, kase, isave)

DLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products. 💅

🎀 Function/Subroutine Documentation

subroutine DLACN2 (integer n, double precision, dimension( * ) v, double precision, dimension( * ) x, integer, dimension( * ) isgn, double precision est, integer kase, integer, dimension( 3 ) isave)

DLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

🫶 Purpose

DLACN2 estimates the 1-norm of a square, real matrix A. Reverse communication is used for evaluating matrix-vector products.

🌈 Parameters

🌟 N

N is INTEGER. The order of the matrix. N >= 1.

🌟 V

V is DOUBLE PRECISION array, dimension (N). On the final return, V = A*W, where EST = norm(V)/norm(W) (W is not returned).

🌟 X

X is DOUBLE PRECISION array, dimension (N). On an intermediate return, X should be overwritten by

A * X,   if KASE=1,
A**T * X,  if KASE=2,

and DLACN2 must be re-called with all the other parameters unchanged. 🌀

This is reverse communication, so the routine is basically passing notes in class: it hands you X, you overwrite it, then you call back with the same everything else. 💌

🌟 ISGN

ISGN is INTEGER array, dimension (N).

🌟 EST

EST is DOUBLE PRECISION. On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be unchanged from the previous call to DLACN2. On exit, EST is an estimate (a lower bound) for norm(A). 💖

🌟 KASE

KASE is INTEGER. On the initial call to DLACN2, KASE should be 0. On an intermediate return, KASE will be 1 or 2, indicating whether X should be overwritten by A * X or A**T * X. On the final return from DLACN2, KASE will again be 0. 🔁

🌟 ISAVE

ISAVE is INTEGER array, dimension (3). ISAVE is used to save variables between calls to DLACN2.

👑 Author

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

🔥 Further Details

Originally named SONEST, dated March 16, 1988. ⏳

This is a thread safe version of DLACON, which uses the array ISAVE in place of a SAVE statement, as follows:

• DLACON → DLACN2
• JUMP → ISAVE(1)
• J → ISAVE(2)
• ITER → ISAVE(3)

🦋 Contributors

Nick Higham, University of Manchester

📚 References

N.J. Higham, "FORTRAN codes for estimating the one-norm ofa real or complex matrix, with applications to condition estimation", ACM Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December 1988.

Definition at line 135 of file dlacn2.f.

💜 Author

Generated automatically by Doxygen for LAPACK from the source code.

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mwah 💋 — sign-off from LAPACK, Version 3.12.0, and the footer path /home/abui...RC/dlacn2.f(3). Bye bestie! 🎀✨