Calculates P0 given a set of parameters
RGHD_P0_calc(sigma_upper, m, r, q)
Int which determine number of iterations for calculation to go through, this is needed to approximate sigma infinity
Parameter of the 2m-RGHD function, this defines number of r and q parameters of the function
R vector containing r parameters from 1:m
R vector containing q parameters from 1:m