Vectorizing a function with two inputs

August 7, 2022

I’m trying to vectorize the following functions:

function f(x)
    z1 = 3*x
    z2 = x^2
    return z1,z2
end

function g(x,y)
    z = 2*x + 3*y*im
    return z
end

My goal, is to have one vector input as x to a function f(x), then take the result of the function g(x,y) and get a single vector output.

When I try to do the following:

x̂ = collect(range(0,10,step=0.01))
g.(f.(x̂))

I get the error:

MethodError: no method matching g(::Tuple{Float64, Float64})

I’m not sure exactly how to make this case work, I guess the fact that the function f returns two values causes the issue, however, it should technically work because the function g takes two inputs.

>Solution :

Since g(x,y) is defined for two arguments but f(x) outputs Tuples, what you want is to Splat the function g before feeding the tuples into it. Splatting means, given a function, return a new function that takes one argument and splats its argument into the original function.

This is achieved by Base.splat or simply Splat in the upcoming Julia releases.

function f(x)
    z1 = 3*x
    z2 = x^2
    return z1,z2
end

function g(x,y)
    z = 2*x + 3*y*im
    return z
end

x̂ = range(0,10,step=0.01)
Base.splat(g).(f.(x̂))

# Or Julia 1.9
Splat(g).(f.(x̂))