The exponential squared kernel $$k(r) = a^2 \, \exp \left (-\frac{r^2}{2\,l^2} \right ) $$

The Matern-3/2 kernel $$k(r) = a^2 \,\left ( 1 + \frac{\sqrt{3}\,|r|}{l} \right ) \exp \left (-\frac{\sqrt{3}\,|r|}{l} \right ) $$

The Matern-5/2 kernel $$k(r) = a^2 \,\left ( 1 + \frac{\sqrt{5}\,|r|}{l} + \frac{5\,r^2}{3\,l^2} \right ) \exp \left (-\frac{\sqrt{5}\,|r|}{l} \right ) $$

The crazyass quasi-periodic kernel $$k(r) = a^2 \, \exp \left (-g^2\,\sin^2\left [ \frac{\pi\,|r|}{P} \right ]-\frac{r^2}{2\,l^2} \right ) $$