Julia global variable throws UndefVarError

Question

The following code fails.

global Θ=1.0
function f(a)
    c=sin(a+θ)
    return c
end
f(1)

UndefVarError: θ not defined

Stacktrace:
 [1] f(a::Int64)
   @ Main ./In[1]:3
 [2] top-level scope
   @ In[1]:6
 [3] eval
   @ ./boot.jl:373 [inlined]
 [4] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
   @ Base ./loading.jl:1196

It has no reason to fails.
Why this is incorrect??
If this doesn't work, I can say that people can't do anything using Julia.

Answer 1

You're using two different characters: the global variable is an uppercase Theta, while the variable you're referring to inside the function is a lowercase theta.

julia> 'Θ'
'Θ': Unicode U+0398 (category Lu: Letter, uppercase)

julia> 'θ'
'θ': Unicode U+03B8 (category Ll: Letter, lowercase)

The lowercase theta θ is a new variable that's never been defined, hence the UndefVarError.

Fixing that:

julia> Θ=1.0
1.0

julia> function f(a)
           c=sin(a+Θ)
           return c
       end
f (generic function with 2 methods)

julia> f(1)
0.9092974268256817

Note that you don't need to mark the global variable as global - it's global by default just by being defined outside any function or other local scope. (global is only needed when you're in a local scope and want to assign to an existing global variable.)