Parameters: 
 method –
Optimization methods. Possible values are:
“Minimize” > minimize by Carl Rasmussen (python implementation of “minimize” in GPML)
“CG” > conjugent gradient
“BFGS” > quasiNewton method of Broyden, Fletcher, Goldfarb, and Shanno (BFGS)
“SCG” > scaled conjugent gradient (faster than CG)
 num_restarts – Set if you want to run mulitiple times of optimization with different initial guess.
It specifys the maximum number of runs/restarts/trials.
 min_threshold – Set if you want to run mulitiple times of optimization with different initial guess.
It specifys the threshold of objective function value. Stop optimization when this value is reached.
 meanRange – The range of initial guess for mean hyperparameters.
e.g. meanRange = [(2,2), (5,5), (0,1)].
Each tuple specifys the range (low, high) of this hyperparameter,
This is only the range of initial guess, during optimization process, optimal hyperparameters may go out of this range.
(5,5) for each hyperparameter by default.
 covRange – The range of initial guess for kernel hyperparameters. Usage see meanRange
 likRange – The range of initial guess for likelihood hyperparameters. Usage see meanRange
