Part of a set of benchmark functions for global optimisation
f(x1,x2)= 0.5 + (sin(sqrt(x12-x22))2 - 0.5) / (1 + 0.001 (x12 + x22))2
The Schaffer F6 function is difficult because the global minimum is surrounded by concentric maxima which are higher closer to the minimum. This is a good test for escaping local minima.
Defined in: Schaffer, J.D. (1985) Some experiments in machine learning using vector evaluated genetic algorithms PhD Thesis, Vanderbilt University, Nashville, TN (USA).
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