Bill Allombert on Wed, 05 Sep 2012 14:39:10 +0200


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Re: polroots stack overflow 

On Mon, Aug 13, 2012 at 03:48:02AM +0200, Sören Lennart Berg wrote:
> Hi,
> the input 
> polroots(94.500000000000000000000000000000000000*z^12 - 5652.0000000000000000000000000000000000*z^11 + 144408.00000000000000000000000000000000*z^10 - 2045344.0000000000000000000000000000000*z^9 + 17354184.000000000000000000000000000000*z^8 - 87874688.000000000000000000000000000000*z^7 + 238393856.00000000000000000000000000000*z^6 - 191892480.00000000000000000000000000000*z^5 - 384723072.00000000000000000000000000000*z^4 - 589317120.00000000000000000000000000000*z^3 + 5892556800.0000000000000000000000000000*z^2 - 6157312000.0000000000000000000000000000*z - 3262720000.0000000000000000000000000000)
> 
> results in a stack overflow even when using almost a gigabyte for the stack.
> Is that a bug or just due to the polynomial having large degree and 'big'
> coefficients?
 
It is a bug which is fixed in the 2.6 branch and will be fixed in PARI 2.5.3
The releant commit is
commit 2a258c781cf273a8fcbd6d8510319441c70d2cbe
Author: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>
Date:   Mon Oct 24 17:36:02 2011 +0200

    fix typo introduced in 7b985ff8a726e89191d2733b9052b2e2c228bfde
    "minor improvements root_error()"
    prod was not re-initialized to 1.

Cheers,
Bill.