Calculates the plotting positions for plotting on probability paper This function is primarily used by the probability plotting functions. The order of the input data is preserved (not sorted).
Inputs: failures - the array or list of failure times right_censored - the array or list of right censored failure times a - the heuristic constant for plotting positions of the form (k-a)/(n+1-2a). Default is a=0.3 which is the median rank method (same as the default in Minitab and Reliasoft).Must be in the range 0 to 1. For more heuristics, see: https://en.wikipedia.org/wiki/Q%E2%80%93Q_plot#Heuristics
Outputs: x,y - the x and y plotting positions as lists