a matrix with the numbers of row and column equal to the lengths of s and t respectively.
The [i, j] element is the reproducing kernel of linear, cubic, quintic, or septic spline
evaluated at (s[i], t[j]).
Arguments
s
a vector of values in [0, 1], at which the kernels are evaluated.
t
an optional vector in [0, 1]. Default is the same as s.