TIME STEP FUNCTION

[Inthanongsone]

Hi,

I'm working on calculating the value of one parameter that occurrs at difference time-scale.

I want to create the time step (look like the one in the figure) to control the calculation.
I can't generate that kind of graph using the IF THEN ELSE, and STEP functions (referred to Vensim model).

Could anyone kindly suggest me what functions can i use to generate this kind of graphs.

I attached a picture and a vensim model for your information.

I really appreciate any help.

Best regards,
Inthan

[tomfid]

I think, generically, your strategy could be something like:

Phase a start = 3
Phase a duration = 4
Phase b start = INITIAL(Phase a start+phase a duration + TIME STEP) ~ time step is optional to prevent concurrence of a & b
Phase b duration = 5

Phase a is started = STEP(1,Phase a start)
Phase a is done = STEP(1,Phase a start+Phase a duration)
Phase a is active = Phase a is started - Phase a is done

Phase b is started = STEP(1,Phase b start)
Phase b is done = STEP(1,Phase b start+Phase b duration)
Phase b is active = Phase b is started - Phase b is done

If there are a lot of activities, this is easier done with arrays - see the project model example in the help system.

If you want the phase durations to vary dynamically or randomly, you need to take a slightly different approach. Create a state machine, with a stock representing each phase's activity state.

[Inthanongsone]

Thank you so very much Tom for your suggestions.

I can't thank you enough.

Regards,
Inthan

[sbeiss]

If you want the phase durations to vary dynamically or randomly, you need to take a slightly different approach. Create a state machine, with a stock representing each phase's activity state.

Hi Tom - this is excatly the situation I'm facing right now. Can you elaborate your proposal of a state machine a bit in more detail please?
Thanks in advance
Stefan

[Administrator]

You need a stock per state. For example,

car is travelling = integ ( car starts travelling - car stops travelling , 0 )

All variables above will be either 0 or 1. You can then add more stocks (eg, car is parked) and the car travels through the states.

Hope this helps.

[tomfid]

If the timing is static, you don't need the state machine. You can just chain together the delays you have:

Code: Select all

Reconnaissance phase=
	PULSE(INITIAL TIME, "Total reconnaissance time (y)" )
Units: Dmnl

**************************************************************
Prospecting Phase=
	PULSE(INITIAL TIME+"Total reconnaissance time (y)","Total prospecting time (y)"
)
Units: Dmnl

**************************************************************

If you want the phases to be nonoverlapping, just add TIME STEP to the start time in the second equation.

[tomfid]

The state machine might look like this:

stateMachine.png (8.79 KiB) Viewed 4798 times

The trigger could be a DELAY FIXED of the previous start, but with that kind of fixed timing, the state machine is really overkill.

Code: Select all

Starting Exploration=
	Prospecting*Trigger for Start of Prospecting/TIME STEP
Units: 1/Month

**************************************************************

Note the division by TIME STEP for dimensional consistency; without that, your model won't work if TIME STEP <> 1.

[tomfid]

See also: http://vensim.com/discrete-stochastic/