Re: FORTRAN memory issues and use of the sum function 'somme'

["Brereton, Ashley" <A.Brereton@liverpool.ac.uk>]

Dear all,

Many thanks for your quick replies.

The glngamma function is exactly what I needed and the gerepilecopy function will be useful for different problems, so this has saved me a massive amount of time!

Thanks again and have a great weekend,

Ash

---

From: Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>
Sent: 25 June 2022 18:15
To: pari-users@pari.math.u-bordeaux.fr <pari-users@pari.math.u-bordeaux.fr>
Subject: Re: FORTRAN memory issues and use of the sum function 'somme'

 

On Sat, Jun 25, 2022 at 04:12:56PM +0000, Brereton, Ashley wrote:
> Hi there,
>
> I was hoping somebody could help with an issue with memory usage.
>
> My code is written in Fortran. In my code, I have a (simplified) loop (see below). The code fails because the pari stack size isn't big enough.
>
> It seems like 'u' is stored at a new memory address for each loop iteration, and so the memory fills up - though I may be wrong!

Yes, this is correct, you should read the chapter 'Garbage collection'
of the documentation.

Let say you want to do the sum

   DO I=1_8,100000_8
        u = gadd(u, stor(I,prec))
   ENDDO

you should do
   av = avma
   DO I=1_8,100000_8
        u = gadd(u, stor(I,prec))
        u = gerepilecopy(av, u);
   ENDDO

or better, only do 'u = gerepilecopy(av, u);' every 1000 iterations or so.

(avma is a global variable from libpari)

Cheers,
Bill.