Cooperative coevolution typo

Whilst re-implementing the paper "A Cooperative Coevolutionary Approach to Function Optimization" by Mitchell Potter and Kenneth De Jong for a Computer Science assignment, I noticed a typo in one of the benchmark functions.

In the paper, the Schwefel function is listed on page 5 as

$$f(x) = 418.9829n + \sum_{i=1}^d x_i \sin{(\sqrt{|x_i|})}$$

Whereas the actual function is

$$f(x) = 418.9829n - \sum_{i=1}^d x_i \sin{(\sqrt{|x_i|})}$$

Notice the sign change in the middle.

I have found 3 references that back this up:

• Schwefel
• Schwefel Function
• Schwefel Function

It's probably also worth noting that one of these sources give the constant to a greater accuracy: 418.982887.