Ventana software support forum

It's often helpful to isolate the sectors of the model (for example, rework cycle and personnel skills), so that they can be tested independently and refined before they are integrated.

A good guideline for modeling is "always be done" - that is, don't add new structure until the existing structure is working and understood. Given that you have questions on a number of structures still, I'd recommend holding schedule pressure constant for now until those are resolved. The...

This is a bug that's triggered by using the Reference Mode tool, but not entering any data. You can remove the reference by saving the model as text (.mdl) and editing it with a text editor to remove the ReferenceMode.vdf lines near the end, like: ///---\\\ :GRAPH Avg :TITLE Avg :SCALE :VAR random x...

Strangely, I can now open the first version of your model. If you want it to run, you need to visit each equation in the editor, hit OK, and say Yes when Vensim offers to update the input list. This will leave you with a model that has no causal arrows, and therefore no dynamics - not very interesti...

Here's how I think of this (hopefully it corresponds with your situation): A released program or module is essentially a compiled snapshot of a codebase at some point in time. It inherits the errors, completeness, and other properties of the codebase at the time of release. Normally, a module is rel...

Not so fast ... You can certainly use data to drive the behavior of your model. You just can't have a variable simultaneously (a) show causal arrows on the diagram and (b) contain only data. A data variable can have a) no equation, in which case it must be supplied in an input data file (vdf) b) a G...

It sounds like you need a stock that serves as a counter. Whenever the research loop is triggered, you flush out the contents (outflow = stock/TIME STEP) and start counting again.

In this version, it looks like "completing tasks" is always 0 due to the (1-effect of misunderstanding...) factor in productivity.

The field could become non-editable if you made the time step a variable expression. Add TIME STEP to your diagram as a shadow variable, and edit it from that.

I can't open the file you posted, but judging by the text, demolition=A FUNCTION OF(demolition,house typology,housing stock,tenancy) ~~| demolition:INTERPOLATE: ~ buildings ~ | You have causal arrows connected to your data variables. You can't have it both ways - if an equation is driven by data, it...

If modules are discrete entities, it seems like you'd need a copy of the task structure for each module. Otherwise you can't distinguish between making 5 modules 10% more complete and making 1 module 50% more complete. If there are just a few modules, you could handle this with copy/paste, but other...

Actually it might be better to consider the release as a "copy" rather than a "move" - something like the following:

See my comment on the other thread.

If I understand your problem framing, I think you'd want something like the following structure. The release switch could be something like a PULSE, if it happens at a particular time, or an IF THEN ELSE statement if it's conditional on the state of the project. The equations for the "releasing...

Since there's no % type or display mode in Vensim, 99~percent and 0.99~dmnl should be different. To avoid percent/fraction conversion errors, I generally create a unit converter variable, "100 percent"==100~percent, and use that. For example: percent real fruit juice = "100 percent&qu...

"Structure" in this context means that if QI must be 0 to 1, the equations that are inputs to QI, and the form in which they are combined, must always produce a result that is 0 to 1. Example 1 (bad): QI = a*schedule_pressure + b*overtime There's no guarantee in general that this will yiel...

Sensitivity analysis will vary the values across simulations, not over time.

I'm unclear on the meaning of the flow from "tasks done" to "work accomplished in module" - is this some kind of release process, where tasks done are declared to be part of a finished module at some point?

An implicit assumption in the FIND ZERO function is that the response of the vector to be zeroed to the control vector to be set meets some reality checks. For example, it needs to be continuous and have a gradient everywhere. Otherwise the algorithm can easily get stuck on flat spots, local minima ...

In this case, the scaling factors should not be 1: zs is a scaling vector for z. After multiplying z by this vector the results should all be of the order of magnitude of 1. zs must be a vector of the same length as x and will often be a vector of ones. http://www.vensim.com/documentation/fn_find_ze...

http://www.vensim.com/documentation/20740.htm
http://www.vensim.com/documentation/ref_custom.htm
http://www.vensim.com/documentation/scaling.htm

There's a RANDOM_ function for generating from the gamma distribution, if that's what you need. There's also the GAMMA_LN function that gives you the log of the gamma function, which can be used to calculate the gamma pdf.

Have you scaled your input vectors to order of magnitude 1? There may be numerical precision issues if not.

If the output is constant, then it seems that your inputs must be constant as well (unless the table function relationships are flat). So, the question is, which of your inputs should be varying, and why? You can implement variation in the inputs with test inputs like STEP, PULSE, or SIN, or a looku...

Also see
http://dspace.mit.edu/handle/1721.1/11105

Is the oscillation you want a test input in schedule pressure, or desired behavior of quality?