This is a brute-force method to make a first estimate of the optimal model parameters.
The matrix 'P' holds rows of possible parameter values.
Each row is passed to the 3, 5, and 7 parameter models and the sum of residuals squared is calculated for the given times (obj$time) and thresholds (obj$thrs).
So for each row in 'P' there is a score for each model. Then for each model the row which yields the lowest SSE is chosen as a starting point for optimisation. The optimised parameters are stored in 'param' and once the three parameter arrays have been found their AICc scores are found and returned as AIC.