SRC/zlassq.f90(3)

🌸 NAME 🌸

okay bestie, welcome to the LAPACK library functions manual page for SRC/zlassq.f90(3) 💖. This page is all about SRC/zlassq.f90 — specifically the zlassq subroutine that updates a sum of squares represented in scaled form. No cap, that’s the whole name-and-purpose vibe.

✨ 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.

🦋 Purpose 🦋

okay so 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. 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, this holds the scale value from 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, this holds the sumsq value from 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 💅

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okay that’s the page, bestie — footer info is LAPACK Version 3.12.0 and SRC/zlassq.f90(3), and yes it’s giving very official library manual energy 💖✨