std.math performance (SSE vs. real)

[Russel Winder via Digitalmars-d]

On Sat, 2014-06-28 at 03:42 -0700, Walter Bright via Digitalmars-d
wrote:
> On 6/28/2014 2:47 AM, francesco cattoglio wrote:
> > When you need accuracy, 999 times out of 1000 you change the numerical
> > technique, you don't just blindly upgrade the precision.
> 
> I have experience doing numerical work? Upgrading the precision is the first 
> thing people try.

Nonetheless, algorithm and expression of algorithm are often more
important. As proven by my Pi_Quadrature examples you can appear to have
better results with greater precision, but actually the way the code
operates is actually the core problem: the code I have written does not
do things in the best way to achieve the best result as a given accuracy
level..

[…]
> 
> Errors accumulate very rapidly and easily overwhelm the significance of the answer.

I wonder if programmers should only be allowed to use floating point
number sin their code if they have studied numerical analysis?
> 
> > Especially the numerical analysts themselves will pay that price. 64 bit HAS to
> > be as fast as possible, if you want to be competitive when it comes to any kind
> > of numerical work.
> 
> Getting the wrong answer quickly is not useful when you're calculating the 
> stress levels in a part.

[…]
> Again, I've done numerical programming in airframe design. The correct answer is 
> what matters. You can accept wrong answers in graphics display algorithms, but 
> not when designing critical parts.

Or indeed when calculating anything to do with money.

-- 
Russel.
=============================================================================
Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder at ekiga.net
41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel at winder.org.uk
London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder
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