# griewank.mod	OBR2-AN-2-4
# Original AMPL coding by Elena Bobrovnikova (summer 1996 at Bell Labs).

# Ref.: C. Jansson and O. Knueppel, "A Global Minimization Method:
# the Multi-Dimensional Case", Technische Informatik III,
# TU Hamburg-Hamburg, Jan. 1992, p. 47 (problem "G2").

# Number of variables:  2
# Number of constraints:  4
# Objective nonconvex, noseparable
# Simple bound constraints

# The global minimum is Fgre = 0, x = (0,0). There are lots of local minima.


var x{1..2} <= 100, >= -100, := 1;

minimize Fgre:
  (x[1]^2 + x[2]^2) / 200 - cos(x[1]) * cos(x[2] / sqrt(2)) + 1;

.