Dear Luis, (hope I guessed your name correctly),
Thanks for your reply. It's very interesting, although not easy to
understand.
In any case, I am more interested in C level and SAGE/C interface.
Also, I am failing to understand when NTL will enter the "error path".
For instance,
consider the following C++ code:
#include "NTL/ZZ_pX.h"
NTL_CLIENT
ZZ_p::init( power2_ZZ(128) );
ZZX p;
SetCoeff(p, 0, power2_ZZ(127));
SetCoeff(p, 1, power2_ZZ(126));
ZZ_pX pp = to_ZZ_pX(p);
ZZ_p::init( power2_ZZ(3) );
ZZ_pX pp2 = to_ZZ_pX(p);
pp2 = pp; // (*)
I would expect the (*) statement to result in an error, since pp2 was
allocated with smaller (and fixed) size than pp.
However, the program finishes normally! When I tried to debug it, I
ended up in macros defining vector classes, where debugging is
impossible...
Thanks,
B/
On Mar 24, 5:19 pm, luisfe <lftab...@yahoo.es> wrote:
> On 24 mar, 12:53, Barukh Ziv <barukh....@gmail.com> wrote:
>
>
>
>
>
> > Guys,
>
> > Thank you for the quick reply. I will answer to both questions:
>
> > > Are you using ntl_ZZ_p or ntl_ZZ_pE? I have experienced the same type
> > > of errors with the latter (due to bad manipulations of
> > > ntl_ZZ_pEContext by myself.
>
> > Yes, I experience problems while using ZZ_pE as in this case NTL does
> > block allocation, and cannot re-allocate a single ZZ_p.
>
> > On Mar 24, 11:08 am, Mike Hansen <mhan...@gmail.com> wrote:
>
> > > Are you able to post the code that causes this problem? That would
> > > help a lot with trying to figure out what's going on.
>
> > > --Mike
>
> > Mike, unfortunately, the code is too complicated to be presented here,
> > but I will try my best to explain what kind of the problem
> > I am facing. Basically, the problem occurs once an ZZ_pX was created
> > with a certain modulus N, and then assigned from another
> > ZZ_pX created with a bigger modulus N' > N. Semantically, consider the
> > following algorhtm:
>
> > ZZ_pE a, ap;
> > // Initialize ap
>
> > while (precision < max_precision)
> > {
> > a = f(ap); // *
> > ap = a; // **
>
> > precision++;
>
> > }
>
> > where calculations in f() are done with modulus 2^precision. IMHO,
> > both statements (*) and (**) may lead to an error, as they should be
> > overwritten with bigger array.
>
> > This is essentially a problem stated in the aforementioned SAGE doc
> > page on p-adic element. So, I wonder, do you know any good ways to
> > overcome this? In particular, is there a way to explicitly re-allocate
> > a previously allocated ZZ_pX object?
>
> Yes you can, altought if your code is very low level I am not sure on
> the impact.
>
> Consider this:
>
> sage: a = ntl.ZZ_pContext(128)
> sage: polynomial = ntl.ZZ_pX([1,2,3,4,5],a)
>
> sage: for i in range(128):
> ....: a = ntl.ZZ_pContext(a.modulus()*2)
> ....: f = f.convert_to_modulus(a)
> ....:
> sage: f
> [1 2 3 4 5]
> sage: f.get_modulus_context()
> NTL modulus 43556142965880123323311949751266331066368
>
> This create a new polynomial modulus the right context.However, this
> will not work to change context in ZZ_pEX in which you are changing
> your defining polynomial (succesive residuals of a p-adic f)
>
> For example,
> Suppose f = 15 + x ^2 and you want an algorithm to compute in
> (ZZ/2^nZZ)[x] / ( f(x) )
>
> sage: p = ntl.ZZ_pContext(2)
> sage: f = [15, 0, 1]
> sage: pe = ntl.ZZ_pEContext( ntl.ZZ_pX(f, p) )
> sage: poly = ntl.ZZ_pEX([[1], [0], [0,1]], pe)
> sage: p2 = ntl.ZZ_pContext(4)
> sage: poly = poly.convert_to_modulus(p2)
> sage: sage: poly.get_modulus_context()
> NTL modulus [1 0 1] (mod 4)
>
> Which is not what we want. Instead, you could add to ntl_ZZ_pEX a
> function like (In the following function one should omit the pcontext
> input c and use cE.get_pc() instead)
>
> def convert_to_pE(self, ntl_ZZ_pContext_class c,
> ntl_ZZ_pEContext_class cE):
> """
> Returns a new ntl_ZZ_pE which is the same as self, but
> considered modulo a different pE (but the SAME polynomial).
> """
> cE.restore_c()
> cdef ntl_ZZ_pEX ans = PY_NEW(ntl_ZZ_pEX)
> _sig_on
> ZZ_pEX_conv_modulus(ans.x, self.x, c.x)
> _sig_off
> ans.c = cE
> return ans
>
> with this function, the previous example would be:
>
> sage: p = ntl.ZZ_pContext(2)
> sage: f = [15, 0, 1]
> sage: pe = ntl.ZZ_pEContext( ntl.ZZ_pX(f, p) )
> sage: poly = ntl.ZZ_pEX([[1], [0], [0,1]], pe)
> sage: p2 = ntl.ZZ_pContext(4)
> sage: pe2 = ntl.ZZ_pEContext( ntl.ZZ_pX(f, p2) )
> sage: poly = poly.convert_to_pE(p2, pe2)
> sage: poly.get_modulus_context()
> NTL modulus [3 0 1] (mod 4)
>
> Another question: does NTL
>
> > perform an automatic garbage collection in any way?
>
> No idea, sorry- Hide quoted text -
>
> - Show quoted text -
--
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