- **GMP-ECM**
(*https://www.mersenneforum.org/forumdisplay.php?f=55*)

- - **using libecm from python**
(*https://www.mersenneforum.org/showthread.php?t=7923*)

using libecm from pythonHello,
I am writing a wrapper for ecm using python and pyrex. I have successfully wrapped the ecm_factor method defined in ecm.h but am a bit confused about the factors it sometimes finds. If I call ecm_factor(f, n, B1, NULL), the factor it finds is sometimes equal to n. I thought it was supposed to return you a nontrivial factor. Cheers, Yi |

It depends on the parameters. Bad sigma values can cause the trivial factor [I]N[/I] to be found, specifically sigma=0,1,2,3 and 5, afaik. Also, if all prime factors in [I]N[/I] are relatively small and your B1 value is high enough, ECM can find all factors simultaneously and hence return [I]N[/I] as the factor.
Alex |

Aha, I see. Thanks for your clear explanation.
Yi |

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