Optimizer for acquisition function

[Aditya Subramanyam]

Use of brute-force non-ideal for large dimensions - consider using one of the gradient-based techniques (available from scipy's 'optimize' package)

[Balaji Pokuri]

This shall be addressed by allowing the user to change the acquisition_function_optimizer, just like how the user can change the kernel_function The default will be changed from brute to a better robust method.

Should be easy to change without much effect on the user code. (easy backward compatibility)

[Balaji Pokuri]

[major] Added default acquisition function optimizer

No major change to the user code.. added functionality

• Uses powell method instead of brute. should resolve #31
• general function signature: acq_optimizer(func: Callable, x0: np.array, bounds, func_deriv: Callable=None) -> np.array:

→ <<cset ae87cb682d86>>

[Balaji Pokuri]

Still has issues with the powell optimizer. Could lead to problems in lower dimensions or with small kappa

[Balaji Pokuri]

One potential method is to use a default acquisition optimizator as a generator of local optima of acquisition and check if either of them is useful