gnuplot-info

[Gnuplot-info] avoid double function evaluation on '+' special file

[<fi...@ig...>]

Dear Gnuplot Users,

suppose the following simple gnuplot example snippet which is used to
plot a complex valued function:

   w = 5
   r = 3
   f(t) = r * exp(I * w * t)
   plot sample [t=0:1] '+' u (real(f(t))):(imag(f(t))) w l

here the function f(t) is evaluated twice - not desirable because of
performance. How can this be done with only one evaluation of f(t)?


Thanks for any advice and best regards


Torsten


-- 
------------------------------------------------------------------------
Torsten Finke
fi...@ig...
------------------------------------------------------------------------

Re: [Gnuplot-info] avoid double function evaluation on '+' special file

[Ethan M. <eam...@gm...>]

On Sun, Apr 21, 2024 at 6:31 AM <fi...@ig...> wrote:

> Dear Gnuplot Users,
>
> suppose the following simple gnuplot example snippet which is used to
> plot a complex valued function:
>
>    w = 5
>    r = 3
>    f(t) = r * exp(I * w * t)
>    plot sample [t=0:1] '+' u (real(f(t))):(imag(f(t))) w l
>
> here the function f(t) is evaluated twice - not desirable because of
> performance. How can this be done with only one evaluation of f(t)?
>

    plot sample [t=0:1] '+' u (temp=f(t),real(temp)):(imag(temp)) w l


>
> Thanks for any advice and best regards
>
> Torsten
>

Re: [Gnuplot-info] avoid double function evaluation on '+' special

[Marc C. <mc...@un...>]

On Sun, Apr 21, 2024 at 11:54:42AM -0700, Ethan Merritt wrote:
>     plot sample [t=0:1] '+' u (temp=f(t),real(temp)):(imag(temp)) w l

aside: it is common in other langages that unfinished expressions allows
line returns. it would be nice to have it in gnuplot so we can write

	w=5; r=3
	f(t) = r * exp(I * w * t)
	plot sample [t=0:1] '+' u (
		temp=f(t),
		real(temp)):(imag(temp)
	) w l

regards

-- 
Marc Chantreux
Pôle CESAR (Calcul et services avancés à la recherche)
Université de Strasbourg
14 rue René Descartes,
BP 80010, 67084 STRASBOURG CEDEX
03.68.85.60.79

Re: [Gnuplot-info] avoid double function evaluation on '+' special

[Dave H. <da...@ho...>]

On Mon, 22 Apr 2024, Marc Chantreux wrote:

> On Sun, Apr 21, 2024 at 11:54:42AM -0700, Ethan Merritt wrote:
> >     plot sample [t=0:1] '+' u (temp=f(t),real(temp)):(imag(temp)) w l
> 
> aside: it is common in other langages that unfinished expressions allows 
> line returns. it would be nice to have it in gnuplot so we can write
> 
> 	w=5; r=3
> 	f(t) = r * exp(I * w * t)
> 	plot sample [t=0:1] '+' u (
> 		temp=f(t),
> 		real(temp)):(imag(temp)
> 	) w l

Well, a good optimiser would also recognise an invariant expression inside 
a loop, and take it outside :-)  (Which you did)

And as for line returns, I'm waiting for # \
    [ Blah ]
to not be the continuation of a comment; simple, really...

-- Dave