Shekel function
The Shekel function is a multidimensional, multimodal, continuous, deterministic function commonly used as a test function for testing optimization techniques. The mathematical form of a function in  dimensions with  maxima is:

or, similarly,

Global minima 

Numerically certified global minima and the corresponding solutions were obtained using interval methods for up to . References 

Shekel, J. 1971. "Test Functions for Multimodal Search Techniques." Fifth Annual Princeton Conference on Information Science and Systems. See also 
Test functions for optimization

Mathematical optimization
Functions and mappings