The `time` variable in BioCro

Even when using an adaptive ODE solver, run_biocro returns values at evenly spaced time intervals given by the `timestep` parameter. It is assumed that the drivers are provided at intervals spaced by this `timestep`. To prevent user error, run_biocro will check that the `drivers“ are spaced by `timestep` but to do so, the `drivers` must contain a `time`.

Details

When differential modules are passed, BioCro will check that the drivers have a `time` variable that satisfies: `time[n+1] - time[n] = timestep` for all `n` (no checks are required for direct_modules). BioCro assumes that differential modules return rates-of-change in the same units as `timestep`.

Unless using modules which require time to correpond to a calendar time (a date and time), the starting `time[1]` has no special meaning. If `time[1] = 0` then `time` is the amount of time that has passed since the simulation's start (in the same units as `timestep`).

Certain modules expect `time` to specify a date and time with respect to the calendar. For most BioCro simulations, the rates of change are measured per hour, therefore `timestep` has units hour.

Therefore, the time variable is defined as the number of hours that have passed since midnight January 1st of the same year. For example for year 2023: + `time = 0` is '2023-01-01 00:00:00' + `time = 1` is '2023-01-01 01:00:00' + `time = 50`is '2023-01-03 02:00:00' Note in version 3.1.3 and earlier of BioCro `time` counted the number of days rather than hours.