# How to read and understand Julia documentation
**URL:** https://discourse.julialang.org/t/how-to-read-and-understand-julia-documentation/39122
**Category:** New to Julia
**Tags:** question, package
**Created:** [May 8, 2020, 5:23pm UTC](https://discourse.julialang.org/t/how-to-read-and-understand-julia-documentation/39122 "2020-05-08T17:23:01Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Oto\_Brzobohaty](https://discourse.julialang.org/u/Oto_Brzobohaty)
#### Post date: [May 8, 2020, 5:23pm UTC](https://discourse.julialang.org/t/how-to-read-and-understand-julia-documentation/39122/1 "2020-05-08T17:23:01Z")
# 1. Example:
I tried to use Optim package to implement [MATLAB fminsearch](https://www.mathworks.com/help/matlab/ref/fminsearch.html) I have found it in the Optim [documentation](https://julianlsolvers.github.io/Optim.jl/v0.9.3/algo/nelder_mead/) and I tried to follow it:
```julia
using Optim
struct MatlabSimplexer <: Optim.Simplexer
a::Float64
b::Float64
end
MatlabSimplexer(;a = 0.00025, b = 0.05) = MatlabSimplexer(a, b)
function Optim.simplexer{T, N}(A::MatlabSimplexer, initial_x::Array{T, N})
n = length(initial_x)
initial_simplex = Array{T, N}[initial_x for i = 1:n+1]
for j = 1:n
initial_simplex[j+1][j] += initial_simplex[j+1][j] == zero(T) ? S.b * initial_simplex[j+1][j] : S.a
end
initial_simplex
end
```
and I got this `ERROR: UndefVarError: T not defined`
How to read and understand this `Optim.simplexer{T, N}`?
How to do it properly?
# 2. Example:
[LIBSVM.jl](https://github.com/mpastell/LIBSVM.jl) package ask you to follow `?svmtrain` for options, which is:
```julia-auto
svmtrain{T, U<:Real}(X::AbstractMatrix{U}, y::AbstractVector{T}=[];
svmtype::Type=SVC, kernel::Kernel.KERNEL=Kernel.RadialBasis, degree::Integer=3,
gamma::Float64=1.0/size(X, 1), coef0::Float64=0.0,
cost::Float64=1.0, nu::Float64=0.5, epsilon::Float64=0.1,
tolerance::Float64=0.001, shrinking::Bool=true,
probability::Bool=false, weights::Union{Dict{T, Float64}, Compat.Nothing}=nothing,
cachesize::Float64=200.0, verbose::Bool=false)
```
and a lot of listed parameters, e.g.
```
• svmtype::Type=LIBSVM.SVC: Type of SVM to train SVC (for C-SVM), NuSVC OneClassSVM, EpsilonSVR or NuSVR. Defaults to
OneClassSVM if y is not used.
• kernel::Kernels.KERNEL=Kernel.RadialBasis: Model kernel Linear, polynomial, RadialBasis, Sigmoid or Precomputed.
• degree::Integer=3: Kernel degree. Used for polynomial kernel
• gamma::Float64=1.0/size(X, 1) : γ for kernels
```
Could you please explain to me how to set `svmtype` and `kernel`? And what is `svmtrain{T, U<:Real}`?
---
### Author:  [@pixel27](https://discourse.julialang.org/u/pixel27)
#### Post date: [May 8, 2020, 8:19pm UTC](https://discourse.julialang.org/t/how-to-read-and-understand-julia-documentation/39122/2 "2020-05-08T20:19:49Z")
I don’t know Optim, but for the error change:
```julia
function Optim.simplexer{T, N}(A::MatlabSimplexer, initial_x::Array{T, N})
```
to:
```julia
function Optim.simplexer(A::MatlabSimplexer, initial_x::Array{T, N}) where {T, N}
```
---
### Author:  [@tim.holy](https://discourse.julialang.org/u/tim.holy)
#### Post date: [May 8, 2020, 10:53pm UTC](https://discourse.julialang.org/t/how-to-read-and-understand-julia-documentation/39122/3 "2020-05-08T22:53:36Z")
Those are very old & outdated Optim documentation pages. Recommended procedure is to go to the GitHub page ([https://github.com/JuliaNLSolvers/Optim.jl](https://github.com/JuliaNLSolvers/Optim.jl)) and click on the blue documentation badge.
---
### Author:  [@Oto\_Brzobohaty](https://discourse.julialang.org/u/Oto_Brzobohaty)
#### Post date: [May 9, 2020, 5:53am UTC](https://discourse.julialang.org/t/how-to-read-and-understand-julia-documentation/39122/4 "2020-05-09T05:53:01Z")
Thank you for answer. I will pay more attention to documentation version:-)