# Just iFOD1 and iFOD2 works, FACT not

**URL:** <https://community.mrtrix.org/t/just-ifod1-and-ifod2-works-fact-not/722>\
**Category:** Uncategorized\
**Tags:** tractography\
**Created:** [February 15, 2017, 11:55am UTC](https://community.mrtrix.org/t/just-ifod1-and-ifod2-works-fact-not/722 "2017-02-15T11:55:04Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![rsmith](https://community.mrtrix.org/user_avatar/community.mrtrix.org/rsmith/32/2672_2.png) [@rsmith](https://community.mrtrix.org/u/rsmith)\
**Post date:** [March 6, 2017, 7:41am UTC](https://community.mrtrix.org/t/just-ifod1-and-ifod2-works-fact-not/722/9 "2017-03-06T07:41:51Z")

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Ah sorry, I forgot about that one in my response:

The `nulldist` / `nulldist2` algorithms are _supposed_ to be noisy; that’s their defining attribute (“Null Distribution”). I would suggest reading the relevant article that is cited in the `tckgen` command’s [reference section](http://mrtrix.readthedocs.io/en/latest/reference/commands/tckgen.html#references).

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