ZLASSQ(3)

ZLASSQ(3) 💖

Okay bestie, this is a LAPACK manual page from the Library Functions Manual, and it's all about ZLASSQ — a subroutine that updates a sum of squares represented in scaled form. The header/footer path gets shortened to /home/abui.../zlassq.f90(3), and the actual source path in NAME is the long one below. 🫶

NAME

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/zlassq.f90

That's literally the NAME section: the source file path. ✨

SYNOPSIS

Functions/Subroutines

subroutine ZLASSQ (n, x, incx, scale, sumsq)

ZLASSQ updates a sum of squares represented in scaled form. 💅

Function/Subroutine Documentation

subroutine ZLASSQ (integer n, complex(wp), dimension(*) x, integer incx,
       real(wp) scale, real(wp) sumsq)

ZLASSQ updates a sum of squares represented in scaled form. (Yes, it says it again — iconic repetition, no notes.) 👑

Purpose

ZLASSQ returns the values scale_out and sumsq_out such that:

(scale_out**2)*sumsq_out = x( 1 )**2 +...+ x( n )**2 + (scale**2)*sumsq,

where x( i ) = X( 1 + ( i - 1 )*INCX ). The value of sumsq is assumed to be non-negative.

scale and sumsq must be supplied in SCALE and SUMSQ, and scale_out and sumsq_out are overwritten on SCALE and SUMSQ respectively.

Parameters

• N — N is INTEGER. The number of elements to be used from the vector x.
• X — X is DOUBLE COMPLEX array, dimension (1+(N-1)*abs(INCX)). The vector for which a scaled sum of squares is computed. And the indexing is:

x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.

• INCX — INCX is INTEGER. The increment between successive values of the vector x.
  • If INCX > 0, X(1+(i-1)*INCX) = x(i) for 1 <= i <= n
  • If INCX < 0, X(1-(n-i)*INCX) = x(i) for 1 <= i <= n
  • If INCX = 0, x isn't a vector so there is no need to call this subroutine. If you call it anyway, it will count x(1) in the vector norm N times.
• SCALE — SCALE is DOUBLE PRECISION. On entry, the value scale in the equation above. On exit, SCALE is overwritten by scale_out, the scaling factor for the sum of squares.
• SUMSQ — SUMSQ is DOUBLE PRECISION. On entry, the value sumsq in the equation above. On exit, SUMSQ is overwritten by sumsq_out, the basic sum of squares from which scale_out has been factored out.

Author

Edward Anderson, Lockheed Martin. 👑

Contributors:

• Weslley Pereira, University of Colorado Denver, USA
• Nick Papior, Technical University of Denmark, DK

Further Details

Anderson E. (2017)
Algorithm 978: Safe Scaling in the Level 1 BLAS
ACM Trans Math Softw 44:1--28
https://doi.org/10.1145/3061665

Blue, James L. (1978)
A Portable Fortran Program to Find the Euclidean Norm of a Vector
ACM Trans Math Softw 4:15--23
https://doi.org/10.1145/355769.355771

Definition at line 123 of file zlassq.f90. 📌

Author

Generated automatically by Doxygen for LAPACK from the source code.

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That's the whole page, bestie 💖 — LAPACK Version 3.12.0, source path /home/abui.../zlassq.f90(3). The footer has no date listed, so the cute sign-off is just version + source vibes. 🎀