The docstring explanation about some kernels contradicts the implementation:

1. Rational quadratic kernel: in the introduction page http://scikit-learn.org/stable/modules/gaussian_process.html#gp-kernels, the power is "alpha", but in the implementation, it is -1*alpha. (see line 1470).

2. "ExpSineSquare" kernel: in the docstring (http://scikit-learn.org/stable/modules/gaussian_process.html#gp-kernels) the positions of parameter "l" and power of 2 are wrong. It should be "exp(-2(sin(pi/p *d(x_i,x_j))/l)^2)", rather than "exp(-2sin(pi/p *d(x_i,x_j))/l)^2".