ifactor problem with new update
05-30-2014, 08:05 PM
Post: #1
 Peter Van Roy Junior Member Posts: 21 Joined: Jan 2014
ifactor problem with new update
With the new update, I get the following (occurs with various inputs, the following is just one example):

ifactor(2ˆ101+5)

On the TI-nspire, factor(2ˆ101+5) works just fine (and the factorization it gives is correct, as a multiplication proves).

Peter

PS: Is there an official bug submission site for the Prime? I hate to create a new thread whenever I find a bug.
05-30-2014, 08:17 PM
Post: #2
 Francois Lanciault Member Posts: 116 Joined: Dec 2013
RE: ifactor problem with new update
This is strange because ifactor(2^128+1) works, even if the number to factorize is bigger.

F.
05-31-2014, 12:18 AM
Post: #3
 toml_12953 Senior Member Posts: 2,097 Joined: Dec 2013
RE: ifactor problem with new update
(05-30-2014 08:05 PM)Peter Van Roy Wrote:  With the new update, I get the following (occurs with various inputs, the following is just one example):

ifactor(2ˆ101+5)

ifactor(2^102+5) works fine. I wonder what the bug is caused by.

Tom L
Cui bono?
05-31-2014, 01:05 AM
Post: #4
 Helge Gabert Senior Member Posts: 467 Joined: Dec 2013
RE: ifactor problem with new update
This might not be a bug. Depends on how the quadratic sieve factoring algorithm was implemented in the Prime, what the cutoff is for the running time, what primes are selected to be in the factor base, etc. Not all integers of comparable length can be expected to be factored in the same amount of time.
05-31-2014, 06:40 AM
Post: #5
 DMaier Member Posts: 59 Joined: Jan 2014
RE: ifactor problem with new update
By the way:

ifactor(2^101+5)=47*1721*253719757*123536856746739823 (this fails)

ifactor(2^102+5)=3*85060127*19870659260881492319689

ifactor(2^128+1)=59649589127497217*5704689200685129054721

It doesn't fail with either:

ifactor(47*1721*253719757)

or

ifactor(47*1721*123536856746739823)

but the following does fail:

ifactor(253719757*123536856746739823)
05-31-2014, 06:52 AM
Post: #6
 parisse Senior Member Posts: 1,311 Joined: Dec 2013
RE: ifactor problem with new update
I'm going to increase the number of tries for Pollard-rho.
05-31-2014, 07:25 PM
Post: #7
 rprosperi Super Moderator Posts: 6,260 Joined: Dec 2013
RE: ifactor problem with new update
(05-31-2014 06:52 AM)parisse Wrote:  I'm going to increase the number of tries for Pollard-rho.

Oh, of course! The old Pollard-rho count wasn't set right. I should have thought of that....

You amaze me Bernard. In a good way.

--Bob Prosperi
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