Rosenbrock function
In mathematical optimization, the Rosenbrock function is a non-convex function, introduced by Howard H. Rosenbrock in 1960, which is used as a performance test problem for optimization algorithms It is also known as Rosenbrock's valley or Rosenbrock's banana function.
wikipedia
The function is defined by:
\[ f(x,y)=(a-x)^{2}+b(y-x^{2})^{2}\]
draw3d( enhanced3d=true, palette=[8,4,1], explicit((1-x)^2 + 100*(y-x^2)^2,x,-2,2,y,-1,3) );