HPL_pdlamch(3)

💖 HPL_pdlamch 💖

okay bestie, so this is a page from the HPL Library Functions manual — like, HPL_pdlamch(3) — and honestly? it's giving machine whisperer energy. it's the girl who asks your computer what numbers it can actually handle. no cap. ✨

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🌸 NAME 🌸

HPL_pdlamch — determines machine-specific arithmetic constants. she's the vibe check for your floating point, fr fr 💅

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🎀 SYNOPSIS 🎀

#include "hpl.h"

double HPL_pdlamch( MPI_Comm COMM, const HPL_T_MACH CMACH );

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🦋 DESCRIPTION 🦋

HPL_pdlamch determines machine-specific arithmetic constants. basically she goes up to your hardware and is like "so what's tea, what are your limits" and your hardware spills everything. 😭💖

here's the whole roster of constants she can hand you:

• the relative machine precision (eps)
• the safe minimum (sfmin) — the way it's defined is that 1/sfmin does not overflow 👑
• the base of the machine (base)
• the precision (prec)
• the number of (base) digits in the mantissa (t)
• whether rounding occurs in addition (rnd = 1.0 and 0.0 otherwise)
• the minimum exponent before (gradual) underflow (emin)
• the underflow threshold (rmin) — that's base**(emin-1)
• the largest exponent before overflow (emax)
• the overflow threshold (rmax) — that's (base**emax)*(1-eps)

like, she's the main character of "what is this machine even capable of". iconic behavior. 🔥

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✨ ARGUMENTS ✨

• COMM (global/local input) MPI_Comm — the MPI communicator identifying the process collection. yes bestie, this is the group chat. the process collection is literally a group chat. 🫶
• CMACH (global input) const HPL_T_MACH — specifies the value to be returned by HPL_pdlamch. pick your fighter:

   = HPL_MACH_EPS,   HPL_pdlamch := eps (default)
   = HPL_MACH_SFMIN, HPL_pdlamch := sfmin
   = HPL_MACH_BASE,  HPL_pdlamch := base
   = HPL_MACH_PREC,  HPL_pdlamch := eps*base
   = HPL_MACH_MLEN,  HPL_pdlamch := t
   = HPL_MACH_RND,   HPL_pdlamch := rnd
   = HPL_MACH_EMIN,  HPL_pdlamch := emin
   = HPL_MACH_RMIN,  HPL_pdlamch := rmin
   = HPL_MACH_EMAX,  HPL_pdlamch := emax
   = HPL_MACH_RMAX,  HPL_pdlamch := rmax

where 👇

   eps   = relative machine precision,
   sfmin = safe minimum,
   base  = base of the machine,
   prec  = eps*base,
   t     = number of digits in the mantissa,
   rnd   = 1.0 if rounding occurs in addition,
   emin  = minimum exponent before underflow,
   rmin  = underflow threshold,
   emax  = largest exponent before overflow,
   rmax  = overflow threshold.

💡 and yeah, HPL_MACH_EPS is the default — if you don't say anything, she just gives you eps. lowkey the most popular order at the drive-thru. 🍓

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🌈 sign-off 🌈

and that's the whole page bestie!! this one's from HPL 2.2, dated February 24, 2016 — so it's vintage vintage, but she ate and left no crumbs. go ask your machine what it's made of. mwah 💜✨🧚