Input (pre-processing)

Time & output

The page combines the Time Information and Print Information dialogs of HYDRUS-1D: the simulated period, the limits of the adaptive time step and the times at which results are stored.

Time discretization

Input	HYDRUS	Description
Initial time step Δt	dt	First time step [T]; the step then adapts to the convergence of the iteration.
Minimum time step	dtMin	Smallest allowed time step [T].
Maximum time step	dtMax	Largest allowed time step [T].
Multiplication factor (few iterations)	dMul	Factor > 1 (1.3) applied when the iteration converged within the lower optimal iteration range.
Multiplication factor (many iterations)	dMul2	Factor < 1 (0.7) applied when the iteration needed more than the upper optimal iteration range.
Lower / upper optimal iteration range	ItMin, ItMax	3 and 7 by default.
Initial time, final time	tInit, tMax	Simulated period [T].

The time step is adjusted automatically (time step control): after a step that converged in at most ItMin iterations it is multiplied by dMul, after a step that needed at least ItMax iterations by dMul2; if the iteration does not converge within the maximum number of iterations (Iteration criteria) the step is repeated with Δt/3. Time steps always end at print times and at the times of the time-variable boundary records. The solute and heat transport can limit the step further (Courant number).

Printing

Input	Description
Print times	Times at which profiles, the mass balance and the results pages store values; comma- or blank-separated. Generate equidistant print times creates 10 times between the initial and the final time.
Store time-level info every n-th step	nPrStep: thins the time-level tables (T_LEVEL, Obs_Node).
Write extended flux table T_Level1	lFluxOut: potential and actual fluxes and further cumulative values (output files).
Additionally print at regular intervals	lPrintD with the interval tPrintInt.

Hints

A small initial time step (e.g. 0.001 d) helps the first steps of infiltration into dry soil; the program enlarges it quickly.
dtMax limits the smoothness of the output and the accuracy at strong changes of the boundary conditions; values of 1/10 of the shortest boundary record are a reasonable start.
Many print times cost memory (all profiles are kept in memory).