SRC/dlassq.f90(3)

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okay bestie, welcome to SRC/dlassq.f90(3) from the Library Functions Manual — she’s a Fortran subroutine and honestly? iconic. 💖

🌸 NAME 🌸

SRC/dlassq.f90 — that’s the name, periodt. 🎀

✨ SYNOPSIS ✨

🧚 Functions/Subroutines 🧚

Here’s the call shape, no cap:

       subroutine dlassq (n, x, incx, scale, sumsq)
           DLASSQ updates a sum of squares represented in scaled form.

💅 Function/Subroutine Documentation 💅

🦋 subroutine dlassq 🦋

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

DLASSQ updates a sum of squares represented in scaled form.

🌈 Purpose 🌈

okay so DLASSQ 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 PRECISION 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, 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: ⭐

Definition at line 123 of file dlassq.f90.

🫶 Author 🫶

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mwah 💋 — this cutie came from LAPACK Version 3.12.0, page SRC/dlassq.f90(3), and that’s the footer energy, bestie. 🦋✨

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