# Stochastic simulation error

**URL:** <https://discourse.julialang.org/t/stochastic-simulation-error/58692>\
**Category:** Modelling & Simulations\
**Tags:** distributions, matrices, interactivity, random\
**Created:** [April 6, 2021, 3:16pm UTC](https://discourse.julialang.org/t/stochastic-simulation-error/58692 "2021-04-06T15:16:54Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jailton](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@jailton](https://discourse.julialang.org/u/jailton)\
**Post date:** [April 6, 2021, 3:16pm UTC](https://discourse.julialang.org/t/stochastic-simulation-error/58692/1 "2021-04-06T15:16:54Z")

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Hello,

I am newbie in Julia, trying to run a MCMC algorithm, but I getting some complaints about the parameters of the gamma distribution (which are supposed to be \> 0), but they are, so I don’t understand this complaints. My code is below:

```julia
using Random, Distributions

# Data

M=52
NN=30
n=26
m=34
x = [49., 5., 17., 2., 39., 84., 7., 0., 35., 36., 1400., 5., 34., 15., 11.,
	2., 1., 39., 8., 101., 2., 148., 1., 68., 31., 1., 20., 118., 91.,
	427.]
dc = [1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 0., 1., 1., 1., 1., 1., 1., 1.,
	1., 1., 1., 1., 1., 1., 1., 1., 1., 0., 0., 0.]
y = [0., 35., 50., 11., 25., 16., 36., 27., 19., 17., 7., 11., 2., 82., 24.,
	70., 15., 16., 50., 22., 45., 18., 4., 1., 40., 57., 0., 1., 20.,
	35., 82., 31., 40., 9., 66., 20., 77., 2., 26., 32., 13., 56., 2.,
	9., 4., 30., 3., 26., 4., 45., 25., 5.]
z = [15., 3., 624., 46., 127., 61., 1350., 312., 24., 10., 1024., 39., 730.,
	136., 1379., 1., 836., 60., 1140., 1153., 54., 47., 0., 43., 971.,
	868., 44., 780., 51., 710., 663., 253., 147., 51., 479., 322., 442.,
	65., 419., 362., 64., 228., 65., 264., 25., 193., 196., 63., 12.,
	103., 60., 43.]
dt = [1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 0., 1., 1., 1.,
	0., 0., 1., 1., 1., 1., 0., 0., 1., 0., 1., 0., 0., 1., 1., 1., 0.,
	1., 0., 1., 0., 0., 1., 1., 1., 0., 1., 0., 0., 1., 1., 0., 0., 0.]

#defining vectors and matrices:
lambda=zeros(Float64,1000)
tau=zeros(Float64,1000)
p=zeros(Float64,1000)
theta=zeros(Float64,(1000, NN))
eta=zeros(Float64,(1000, M))

# setting initial values:
lambda[1]=0.1
tau[1]=0.1
p[1]=3
theta[1,:].=0.1
eta[1,:].=0.1
alpha=0.01
beta=0.01
gama=0.01
delta=0.01

# simulation
for k in 2:1000
	lambda[k]=rand(Gamma(2+NN*p[k-1]+M*p[k-1]+alpha,2+beta+sum(theta[k-1,:])+sum(eta[k-1,:])))
	tau[k]=rand(Gamma(m+gama, delta+sum(eta[k-1,:].*z)))
	p[k]=rand(Gamma(2+lambda[k]*((prod(theta[k-1,:])*prod(eta[k-1,:]))^(1/(M+NN)))^(0.999*(M+NN)),1/gamma(0.999)))
	for i in 1:NN
	theta[k,i]=rand(Gamma(p[k]+dc[i],lambda[k]+x[i]))
	end
	for j in 1:M
		eta[k,j]=rand(Gamma(p[k]+dt[j],lambda[k]+y[j]+tau[k]*z[j]))
	end
end

```

It complains that some of the gamma distributions within the for have parameters not satisfying the definition, but we compute the initial parameters manually they are greater than zero. I can’t see why it is not working. I would appreciate any help. thanks.

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**Author:** ![mauro3](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mauro3/32/292_2.png) [@mauro3](https://discourse.julialang.org/u/mauro3)\
**Post date:** [April 6, 2021, 4:32pm UTC](https://discourse.julialang.org/t/stochastic-simulation-error/58692/2 "2021-04-06T16:32:47Z")

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Hi @jailton, welcome to the Julia forum. Have a read of [Please read: make it easier to help you](https://discourse.julialang.org/t/psa-make-it-easier-to-help-you/14757) and edit your post to have the code-blocks commented.