SRC/dlacn2.f(3)

🦋 SRC/dlacn2.f(3) 🦋

okay so bestie, welcome to the Library Functions Manual page for SRC/dlacn2.f(3) — it's literally the dlacn2 subroutine being its main-character self, and we're gonna get into every parameter, every return, every little thread-safety note. no cap. 💅

💖 NAME 💖

SRC/dlacn2.f

✨ 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 🌸

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 — is INTEGER; it's the order of the matrix, and N >= 1. 💖
• V — is a DOUBLE PRECISION array, dimension (N). On the final return, V = A*W, where EST = norm(V)/norm(W) (W is not returned). ✨
• X — is a DOUBLE PRECISION array, dimension (N). On an intermediate return, X should be overwritten by A * X, if KASE=1, or by A**T * X, if KASE=2, and DLACN2 must be re-called with all the other parameters unchanged. 🔥
• ISGN — is an INTEGER array, dimension (N). 🦋
• 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 — 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 — is an 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 of a 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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✨ okay bestie, that's the whole page — LAPACK Version 3.12.0, SRC/dlacn2.f(3), and yes it's the Library Functions Manual cutie. periodt. 💖