# Making high performance functions with flexible inputs

**URL:** <https://discourse.julialang.org/t/making-high-performance-functions-with-flexible-inputs/15890>\
**Category:** Performance\
**Created:** [October 4, 2018, 5:14pm UTC](https://discourse.julialang.org/t/making-high-performance-functions-with-flexible-inputs/15890 "2018-10-04T17:14:48Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![joshdorrington](https://avatars.discourse-cdn.com/v4/letter/j/f4b2a3/32.png) [@joshdorrington](https://discourse.julialang.org/u/joshdorrington)\
**Post date:** [October 4, 2018, 5:14pm UTC](https://discourse.julialang.org/t/making-high-performance-functions-with-flexible-inputs/15890/1 "2018-10-04T17:14:48Z")

</div>

I’m writing some code to solve a couple of o.d.e systems I’m working with.

At the moment I have some code that looks like this:

```julia
    function timestep_a(init;T=1.,dt=0.0005)
                for t in 0.:dt:T
                    init=init+dt*ode_a(init)
                end
        return init
    end

    function timestep_b(init;T=1.,dt=0.0005)
                for t in 0.:dt:T
                    init=init+dt*ode_b(init)
                end
        return init
    end

 #Foo's equation
 function ode_a(input)
            return input*input-0.5*input
 end

#Bar's equation
function ode_b(arr)
           return -input*input+2*input-4.0
end

```

There is a lot of redundancy in the timestep functions, so I would like to make these one function. However if I do this, and pass the specific ode to solve as an argument, the code can’t optimise as well, and is much slower.

Is there a way to have my cake and eat it? Can I get julia to compile a separate timestep function with the same name for both o.d.es without actually writing it twice?

---

<div class="post-metadata">

**Author:** ![jw3126](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jw3126/32/3086_2.png) [@jw3126](https://discourse.julialang.org/u/jw3126)\
**Post date:** [October 4, 2018, 7:28pm UTC](https://discourse.julialang.org/t/making-high-performance-functions-with-flexible-inputs/15890/2 "2018-10-04T19:28:10Z")

</div>

Usually julia is smart enough, to do this optimization. Are you sure that the redundant version is faster?

```julia
using BenchmarkTools
function timestep(f,init;T=1.,dt=0.0005)
            for t in 0.:dt:T
                init=init+dt*f(init)
            end
    return init
end

function timestep_b(init;T=1.,dt=0.0005)
            for t in 0.:dt:T
                init=init+dt*ode_b(init)
            end
    return init
end

#Foo's equation
function ode_a(input)
    return input*input-0.5*input
end

#Bar's equation
function ode_b(input)
    return -input*input+2*input-4.0
end

init = 1.0
@btime timestep($ode_a, $init)
@btime timestep_b($init)

```

```julia
  10.626 μs (2 allocations: 32 bytes)
  11.576 μs (2 allocations: 32 bytes)

```