Help with creating a custom distribution



I’m very new (2 days) into Julia and I’m having trouble defining and plotting a new distribution using StatPlots. Here’s my attempt (creating Normal(mu, 2*sigma) just to make things easy):

using Distributions, Plots, StatPlots
importall Distributions

type MyDist <: ContinuousUnivariateDistribution
    MyDist(mu, sigma) = new(Float64(mu), Float64(sigma))

pdf(d::MyDist, x::Float64) = pdf(Normal(, 2*d.sigma), x)
rand(d::MyDist) = rand(Normal(, 2*d.sigma))
sampler(d::MyDist) = sampler(Normal(, 2*d.sigma))
logpdf(d::MyDist, x::Real) = logpdf(Normal(, 2*d.sigma), x)
cdf(d::MyDist, x::Real) = cdf(Normal(, 2*d.sigma), x)
quantile(d::MyDist, q::Real) = quantile(Normal(, 2*d.sigma), q)
minimum(d::MyDist) = -Inf
maximum(d::MyDist) = Inf
insupport(d::MyDist, x::Real) = insupport(Normal(, 2*d.sigma), x)
mean(d::MyDist) = mean(Normal(, 2*d.sigma))
var(d::MyDist) = var(Normal(, 2*d.sigma))

When I try plot(MyDist(0, 1)), I get the following error: MethodError: no method matching start(::MyDist). If someone could help that would be awesome. Thanks a lot!


You can’t just plot an instance of MyDist. What would you expect it to plot? The pdf or the cdf?

You can try plotting the pdf like so

plot(x->pdf(MyDist(0,1), x))

By the way, what plotting package are you using (Plots.jl?) and what version of Julia is this? type is no longer valid in Julia 1.0, it’s mutable struct (or just struct).


I’m using StatPlots package, which support plotting a distribution, and Julia 0.6.4… Anyways, what I ended up doing was plotting the pdf as you suggested. Thanks!


Can you plot any of the distributions from Distributions?


Yupyup. Please refer to this:


I didn’t mean “can you” as in is it possible, more like: "if fishix10 tries to plot their own distribution type it doesn’t work, but what if they plot(Normal())" :slight_smile:


Oh sorry. Yes I could. :stuck_out_tongue: