c++ cross k function
cross_kfunc_cpp(dist_mat, start, end, step, Lt, na, nb, wa, wb)
A square matrix with the distances between points
A float, the start value for evaluating the k-function
A float, the last value for evaluating the k-function
A float, the jump between two evaluations of the k-function
The total length of the network
The number of points in set A
The number of points in set B
The weight of the points in set A (coincident points)
The weight of the points in set B (coincident points)