changed lengthscale in equation
@@ -17,7 +17,7 @@ class RBFKernel(Kernel):
\begin{equation*}
k_{\text{RBF}}(\mathbf{x_1}, \mathbf{x_2}) = \exp \left( -\frac{1}{2}
- (\mathbf{x_1} - \mathbf{x_2})^\top \Theta^{-1} (\mathbf{x_1} - \mathbf{x_2}) \right)
+ (\mathbf{x_1} - \mathbf{x_2})^\top \Theta^{-2} (\mathbf{x_1} - \mathbf{x_2}) \right)
\end{equation*}
where :math:`\Theta` is a :attr:`lengthscale` parameter.
