doc: kernel_matern
Matern covariance function for 
Syntax
K = kernel_matern(X,'diag',s,ells,nu) K = kernel_matern(X,Y,s,ells,nu)
Arguments
- X matrix (nx, d) where nx is the number of data points and d is the dimension
- Y matrix (ny, d) or 'diag' for diagonal self covariance
- s scalar (1,1) for covariance scale
- ells vector (1,d) of covariance length-scales
- nu scalar (1,1) for Matern parameter
, available values are 1, 3 and 5
Outputs
- K matrix (nx, ny) or diagonal (nx, 1)