Global variables / performance / data passing

New to Julia
21

So, this code structure would be fine?:

struct Data
  a :: Int64
end

const data = Data(4)

# Function that computes the function value

function computef(x :: Float64, data :: Data)
  f = data.a * x^2
  return f
end

# New function with different call, appropriate for "minimize" below

computef(x :: Float64) = computef(x,data)

# This the routine that requires a "computef(x)" function (dummy example)

function minimize(x)
  fcurrent = computef(x)
  y = x - 0.1
  fnew = computef(y)
  if ( fnew < fcurrent )
    return y, fnew
  else
    return x, fcurrent
  end
end

# Main program

x = 10.
println(" x = ",x," f = ",computef(x,data))
x, f = minimize(x)
println(" x = ",x," f = ",computef(x,data))

At the same time, I understand that most Julia functions would require the function “computef” as a parameter, and this structure would be more natural:

struct Data
  a :: Int64
end

const data = Data(4)

# Function that computes the function value

function computef(x :: Float64, data :: Data)
  f = data.a * x^2
  return f
end

# This the routine that requires a "computef(x)" function (dummy example)

function minimize(x,computef)
  fcurrent = computef(x)
  y = x - 0.1
  fnew = computef(y)
  if ( fnew < fcurrent )
    return y, fnew
  else
    return x, fcurrent
  end
end

# Main program

x = 10.
println(" x = ",x," f = ", computef(x,data))

# Passing the function as an argument, as a closure
x, f = minimize(x, x -> computef(x,data) )

println(" x = ",x," f = ", computef(x,data))

Did I get things right? Is there any performance advice that should be added here?

1 Like
22

That looks good to me (the second version since, like you point out, you don’t want to hardcode the function to optimize).

One small suggestion: It is common in Julia to put the function argument first, like this:

function minimize(computef, x)

That will enable the “do-block-syntax”; a convenient and readable way to create anonymous functions:

x, f = minimize(x) do y
    z = zero(y)
    for n = 1:data.a
      z += y * n
    end
    z
end
3 Likes