SRC/classq.f90(3)

🌸 NAME 🌸

SRC/classq.f90 — hi bestie 💖 this is the SRC/classq.f90(3) page from the Library Functions Manual, and it's all about the classq subroutine. No cap. ✨

✨ SYNOPSIS ✨

🦋 Functions/Subroutines 🦋

• subroutine classq (n, x, incx, scale, sumsq) — CLASSQ updates a sum of squares represented in scaled form.

💅 Function/Subroutine Documentation 💅

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

CLASSQ updates a sum of squares represented in scaled form. 🫶

🌟 Purpose 🌟

Okay so CLASSQ 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. Important vibe check: 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. It's the number of elements to be used from the vector x. 🍓

X

X is COMPLEX array, dimension (1+(N-1)*abs(INCX)). It's 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. It's 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. Not me warning you, but bestie, that's what it does. 😭

SCALE

SCALE is REAL. 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 REAL. 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 classq.f90. 👑

🖋️ Author 🖋️

Generated automatically by Doxygen for LAPACK from the source code.

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okay bestie, that's the whole page 💅✨ the footer tea is LAPACK, Version 3.12.0, source SRC/classq.f90(3) — and there's no date in that footer, so I'm not inventing one, periodt. 🫶🎀