How to fix certain hyperparameters?

[mh510]

hi, sorry for this possible trivial question. how can i fix certain hyperparameters before the optimization? for example, my prior mean function is constant with a certain value, which should be fixed and not changed by the hyperparameter optimization. thank you.

[mh510]

another example: my input vector is 2 dimensional and therefore the kernel function does have 2 lengthscale parameters, lets say i want to fix one of them and the other one should be optimized.