Make demography predetermine mortality at the first step of simulation rather than scheduling multiple times

[RobertManningSmith]

Currently mortality is initially decided at the start of the year. Those who are determined to die do so, those that aren't have their mortality decided again once the next simulation year happens.

We could probably reduce the number of times this happens as follows:

1. Include a simulation length variable in the sim object say N days
2. At the start of the simulation do mortality calculations for each person for the time period that the simulation is being run. (I.e. say we run for 800 days, floor (800 / 365) = 2 (years). Calculate the probability of dying in the simulation for each person at age A as prob_dying(A) + prob_dying(A+1) to cover probability of death for both years)
3. Schedule death for some point in the simulation using existing structures

[RobertManningSmith]

On reflection this may not be preferable. If we end up running multi-year simulations, a person's age wouldn't necessarily be accurately considered in their likelihood of death. If we determine mortality at time step 0, and they are on the boundary of an age bracket, this person's aging will not actually come into play when we determine their mortality for multiple stages in the simulation.

Thinking about this, it may be preferable to actually determine each person's mortality on their birthday

[swise5]

In the context of multi-year simulations, we could consider a kludge where, for each year, you calculate their probability of mortality and either schedule their death (uniformly, should they be projected to die in the next year) or else age them a year and repeat the process, stopping when either their death is scheduled or they have aged past the duration of the simulation.
However, that kind of pre-calculation isn't...wildly in the spirit of ABM. It assumes away any other health conditions or changes in situation (eg cascading health consequences from infections; movement among locations; changes in family structure). I think it's a good option to keep in mind, should we find the aging process to be destroying our processing speed.