Define a Julia function

New to Julia
,
1

My question is about which way is better to define this function:
Way 1:

function α(x, a, b, α_0, Lmin, Lnom, Lmax)
if Lmin <= x < Lnom
return a * (x-Lnom)^2 + α_0
elseif Lnom <= x <= Lmax
return b * (x-Lnom)^2 + α_0
end
end
Way 2:
function α(x)
a, b, α_0, Lmin, Lnom, Lmax = Calculations
if Lmin <= x < Lnom
return a * (x-Lnom)^2 + α_0
elseif Lnom <= x <= Lmax
return b * (x-Lnom)^2 + α_0
end
end

As shown above, I want to define a function α(x). The other
parameters are constants. These constants are calculated outside of α(x).

  1. I want to ask for some suggestions on whether I should put these constants as
    arguments or directly put them within α(x)?
  2. I think it would be more convenient to put them inside of the function (together with related calculations). My concern is, I need to use this function to do repeated optimization. Will this slow my program (since these parameters need to be calculated)?
2

if you gonna repeatedly call α(x) and Calculations does calculation, then you don’t want to repeat calculation inside α(x)

1 Like
3

Depends on what “Calculations” are. The compiler can constant-fold some thing.

4

Thanks. In my case, it’s just some simple calculations like curve fitting from known points and some arithmatic calculations.
And there are some parameters in the calculation that I need to modify for different study cases, that’s why I don’t want to manually assign specific numbers in the function definition.

5

Thanks. Yes, that’s the case. I need to repeatedly call this function in my program.

6

In that case, I would define a data structure (struct) to hold the calculation results. Then write two functions: one (probably a constructor) to initialize the data structure instance d from the parameters, and another function function α(x, d). Or potentially you could make d a callable object (which often makes sense for a curve-fitting result), in which case you could write d(x).

1 Like
7

Thanks for the suggestions. I will try them in my program.
I just thought about simply adding the global keyword inside the function to call
these parameters.
Will this slow my program?

8

If the global variables you are accessing are not constants (i.e., do not have const before their name in their definition), then most surely your code will be slowed.

9

I see. Thanks for the reply.

10

It’s not just performance. Non-constant global variables in any programming language are an obstacle to software engineering in the long run. Google “why global variables bad” for lots of explanations.

2 Likes
11

Thanks!