# Multinomial sampling crashes

**URL:** <https://discourse.pymc.io/t/multinomial-sampling-crashes/6470>\
**Category:** Questions\
**Created:** [December 23, 2020, 2:31pm UTC](https://discourse.pymc.io/t/multinomial-sampling-crashes/6470 "2020-12-23T14:31:31Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![tpaixao](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/tpaixao/32/3468_2.png) [@tpaixao](https://discourse.pymc.io/u/tpaixao)\
**Post date:** [December 23, 2020, 2:31pm UTC](https://discourse.pymc.io/t/multinomial-sampling-crashes/6470/1 "2020-12-23T14:31:31Z")

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Hi all,

I am having pymc3 crash my kernel with a very simple model

with pm.Model() as model:  
ps = pm.Dirichlet(‘ps’, a=np.array([1,0,0]))  
counts = pm.Multinomial(“counts”,n=30,p=ps,observed=[29,1,0])  
trace=pm.sample(1000,tune=500)

If I impose only one job (chains=1) it does not crash the kernel but gives a error “BadInitialEnergy”.

Does anyone have any idea of what could be going on?

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**Author:** ![AlexAndorra](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/alexandorra/32/9142_2.png) [@AlexAndorra](https://discourse.pymc.io/u/AlexAndorra)\
**Post date:** [December 23, 2020, 2:40pm UTC](https://discourse.pymc.io/t/multinomial-sampling-crashes/6470/2 "2020-12-23T14:40:57Z")

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Hi Tiago,  
Yeah, it’s actually a good thing it crashes: the concentration vector of the Dirichlet [has to be strictly positive](https://en.wikipedia.org/wiki/Dirichlet_distribution), but you entered zeros at the second and third positions, so the log probability is `-inf`, making the model impossible to sample from.  
Here is [a post](https://calogica.com/python/pymc3/2018/11/27/dice-polls-dirichlet-multinomial.html) about Dirichlet and Multinomial distributions by @clausherther – that should help you 😉  
Hope this helps 🖖

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<div class="post-metadata">

**Author:** ![tpaixao](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/tpaixao/32/3468_2.png) [@tpaixao](https://discourse.pymc.io/u/tpaixao)\
**Post date:** [December 23, 2020, 2:42pm UTC](https://discourse.pymc.io/t/multinomial-sampling-crashes/6470/3 "2020-12-23T14:42:00Z")

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Thanks!! I totally overlooked that…