Broadcasting slower than for-loop

New to Julia
5

Variables in julia are just labels for objects. The variables can always be changed, but that doesn’t change the underlying data. Nothing is being mutated.

When you write

y = y .^ 2

you’re saying “I want to take my label y and change it so that it now labels the result of y .^ 2.” The operation y .^ 2 allocates a whole new vector. The data y used to label is left unchanged.

For example, let’s make a vector y and then say z = y, and then re-bind y. What ends up happening?

julia> let y = [1, 2, 3]
           z = y
           y = [4, 5, 6]
           z
       end
3-element Vector{Int64}:
 1
 2
 3

At the end of this, z is no longer labelleing the same data as y.

Mutation is different. When you mutate something, you’re changing the actual data that the label is pointing to. E.g.:

julia> let y = [1, 2, 3]
           z = y
           y .= [4, 5, 6]
           z
       end
3-element Vector{Int64}:
 4
 5
 6

In this case, z and y are still labelling the same data, but have both been changed by the mutation.

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