i have tried to do a simple code for MCMC as you see below:
traget(x)= (1/sqrt(2*pi*2^2))*exp((-(x-10)^2)/(2*2^2))
proposal(x)=Normal(x,1)
initial=-40
result=[]
Iteration=10000
chain=zeros(Iteration)
accept_rate= zeros(Iteration)
for i in 1:Iteration
accept=0
current= initial
proposed= rand(proposal(current))
C= traget(proposed)/traget(current)
ratio= min(1, C)
uniform=rand()
if uniform< ratio
push!(result, proposed)
current= proposed
accept+=1
else
current=current
end
chain[i]= current
accept_rate[i]= accept/i
end
my problem is when i want to know how many values have passed the test which i can know by length(result) or just accept but when i type accept it shows me only either 0 or 1 and i want to show the number of the proposed values that have passed the MCMC test
You reset accept to zero at every step of your iteration, therefore it can only ever be 1 (if the last iteration produced a proposal that was accepted) or 0 (if it didn’t).
You prpbably meant to set accept = 0 outside you iteration loop.
If the above code runs in the REPL and if you put accept = 0 outside the loop, don’t forget to change the counting line to
global accept+=1
Looking at your code, I guess, that you put accept=0 into the loop, because you run into some error messages you didn’t fully understand.
If this is the case, you may have some insights reading this: https://docs.julialang.org/en/v1/manual/variables-and-scoping/
