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Old 2008-02-17, 13:39   #1
themaster
 
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Default How much ecm should i do???

how much ecm should i do before switching to msieve
i keep on finding that i have spent more time on ecm than msieve takes
this is with numbers between 85 and 100 digits that i am having this problem
i have did 35 digit ecm on a 97 digit number a couple of days ago and that turned out to be way too much
could people post what rules they would use for switching to msieve
i have searched the forum but found nothing
thanks
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Old 2008-02-17, 14:04   #2
jasonp
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Quote:
Originally Posted by themaster View Post
how much ecm should i do before switching to msieve
i keep on finding that i have spent more time on ecm than msieve takes
this is with numbers between 85 and 100 digits that i am having this problem
i have did 35 digit ecm on a 97 digit number a couple of days ago and that turned out to be way too much
could people post what rules they would use for switching to msieve
i have searched the forum but found nothing
thanks
Let the msieve binary do the ECM for you; it already has tuning that guarantees you won't spend too much time before switching to QS.
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Old 2008-02-17, 15:40   #3
themaster
 
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i do the ecm on multiple pcs so that is not possible
i looked at msieves code and found
Code:
static uint32 choose_max_digits(msieve_obj *obj, uint32 bits) {
 /* choose the amount of work to do. We want the
    chosen digit level to be a small fraction of what
    QS and NFS would need */
 uint32 max_digits = 15;
 if (bits == 0)
  return 0;
 if (obj->flags & MSIEVE_FLAG_DEEP_ECM) {
  if (bits > 220) {
   if (bits < 280)
    max_digits = 20;
   else if (bits < 320)
    max_digits = 25;
   else if (bits < 360)
    max_digits = 30;
   else if (bits < 400)
    max_digits = 35;
   else
    max_digits = 40;
  }
 }
 return max_digits;
}
this seems a bit low to me
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Old 2008-02-17, 16:07   #4
Andi47
 
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Oct 2004
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Quote:
Originally Posted by themaster View Post
i do the ecm on multiple pcs so that is not possible
i looked at msieves code and found
Code:
static uint32 choose_max_digits(msieve_obj *obj, uint32 bits) {
 /* choose the amount of work to do. We want the
    chosen digit level to be a small fraction of what
    QS and NFS would need */
 uint32 max_digits = 15;
 if (bits == 0)
  return 0;
 if (obj->flags & MSIEVE_FLAG_DEEP_ECM) {
  if (bits > 220) {
   if (bits < 280)
    max_digits = 20;
   else if (bits < 320)
    max_digits = 25;
   else if (bits < 360)
    max_digits = 30;
   else if (bits < 400)
    max_digits = 35;
   else
    max_digits = 40;
  }
 }
 return max_digits;
}
this seems a bit low to me
hmmmm... that's roughly what I am doing manually. (I am ECM'ing on multiple PCs too.)

Additionally I do some p-1 and p+1.
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Old 2008-02-17, 16:28   #5
themaster
 
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it probably is just that i am used to doing a lot more
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Old 2008-02-17, 19:41   #6
jbristow
 
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I've heard a 2/7 rule of thumb mentioned before. For a 97-digit number, that would mean stopping ECM at 25 or 30 digits if you're trying to optimize computer time.
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Old 2008-02-17, 20:13   #7
themaster
 
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before this i used 1/3 but it often stretched
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Old 2008-02-17, 21:42   #8
xilman
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Quote:
Originally Posted by jbristow View Post
I've heard a 2/7 rule of thumb mentioned before. For a 97-digit number, that would mean stopping ECM at 25 or 30 digits if you're trying to optimize computer time.
AFAIK, the rulle of thumb is 2/9 for SNFS and 1/3 for GNFS. This latter rule is consistent with the 3/2 relative difficulties ROT for NFS.

Within reason, it doesn't much matter. If the factorization is non-trivial other considerations come into play, such as memory usage and communication overheads.

Paul
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Old 2008-02-18, 10:09   #9
themaster
 
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Quote:
Originally Posted by xilman View Post
AFAIK, the rulle of thumb is 2/9 for SNFS and 1/3 for GNFS. This latter rule is consistent with the 3/2 relative difficulties ROT for NFS.

Within reason, it doesn't much matter. If the factorization is non-trivial other considerations come into play, such as memory usage and communication overheads.

Paul
what would u use for QS
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Old 2008-02-18, 12:02   #10
xilman
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Quote:
Originally Posted by themaster View Post
what would u use for QS
As I said, it doesn't much matter. QS is only competitive below 100 digits or thereabouts. I'd probably go to around 30 digits or so.


Paul
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Old 2008-02-18, 12:25   #11
themaster
 
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thanks
this should speed me up quite a bit so i can find more 100 digit RHPs
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