Create kernel matrix for each variable in the formula.
parse_kernel_variable(kern_var_name, kern_func, data, data_new = NULL)
(vector of characters) Names of variables in data to create the kernel matrix from. Must be a single term that is either of the form \(x\) (a single linear term) or \(k(x1, x2, \dots)\) (a kernel term that may contain multiple variables).
(function) A kernel function. Will be overwritten to linear kernel if the variable doesn't contain 'k()'.
(data.frame, n*d) A data.frame, list or environment (or object coercible by as.data.frame to a data.frame), containing the variables in formula. Neither a matrix nor an array will be accepted.
(data.frame, n_new*d) New data for computing predictions.
(matrix, n*n) The kernel matrix corresponding to the variable being computed.