Hello at first i want to introdue myself a little, because i am new here. My name is Christoph and i write my diploma thesis in university at the moment. One part of this thesis is to design an system dynamics modell with vensim for a the complaint management of a company. So there were are. I have already designed the main structure of the model, there are no equation errors and its possible to simulate the model. Also the results of the simulation are goog in my opinion. But i have these unit errors, and i can not solve this problem. If i solve the unit error at one part of the model there will be another. I have spent already three days on this problem and i think its not a big one, so i would be very thankful if someone will have a look to my model or give me a straight tip to solve it by myself, ohterwise i will get problems to finish my thesis at the right time. Sorry for my english and thank you very much already.
Best regards Christoph
[Edited on 6-12-2009 by Christoph]The unit Stk in the model means piece
[Edited on 6-12-2009 by Christoph]
Problems with unit check
Problems with unit check
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bob@vensim.com
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For example
Costs by handling of a complaint =
( Costs per customer complaints
* Realized complaints )
"Costs by handling of a complaint" needs to have units Euro/Month
"Costs per customer complaints" needs to have units Euro/Complaint (note that using Complaint in this way would prevent it from being a variable name)
"Realized Complaints" needs to have units Complaint/Month
The first step is to differentiate between stocks and flows - if levels or stocks have units Complaint, the flows must have units Complaint/Month.
Hope that helps.
Costs by handling of a complaint =
( Costs per customer complaints
* Realized complaints )
"Costs by handling of a complaint" needs to have units Euro/Month
"Costs per customer complaints" needs to have units Euro/Complaint (note that using Complaint in this way would prevent it from being a variable name)
"Realized Complaints" needs to have units Complaint/Month
The first step is to differentiate between stocks and flows - if levels or stocks have units Complaint, the flows must have units Complaint/Month.
Hope that helps.
units errors
Hi Christoph
To avoid the problems you are facing, it is better to write down in words the problem you try to develop and then build an influence diagram or causal loop diagram of your problem without equations but with dimensionnal units. You will realize that dimensions are independant from the equations and are dependant from the structure of the problem, the reason why you can decide which units to choose before you write the equations. Doing this helps too avoiding structural bugs.
Regards.
JJ
To avoid the problems you are facing, it is better to write down in words the problem you try to develop and then build an influence diagram or causal loop diagram of your problem without equations but with dimensionnal units. You will realize that dimensions are independant from the equations and are dependant from the structure of the problem, the reason why you can decide which units to choose before you write the equations. Doing this helps too avoiding structural bugs.
Regards.
JJ
unit errors
Some quick remarks but certainly not complete considering your model.
You should avoid variables with only one variable influencing it. It does not add anything and makes the sketch more complex than it needs to be. There needs to be a time to complete the customers complaints that will too solve a unit error.
The notion of deceleration of generating procceds is not clear for me and what comes along with it. The naming of variables is important. By example 'costs by handling of a complaint' is misleading and should be renamed 'costs of handing complaints'. Most important if you click on the loops gnerator you only find a short loop that describes a model with nearly no dynamic at all. When one looks at the problem in general, it seems obvious that there should be some loops involving the number of customer complaints and the customer value whatever is the customer value description.
It is here that one sees the utility of a clear and complete description with words of the problem and one or two more or less higher level description diagram to help clarify the problem in question.
It would be too of extreme utility to build reality checks of the problem that would highly influence the credibility of your model (and your grading!) if it has to be presented to your examinators.
Regards.
JJ
You should avoid variables with only one variable influencing it. It does not add anything and makes the sketch more complex than it needs to be. There needs to be a time to complete the customers complaints that will too solve a unit error.
The notion of deceleration of generating procceds is not clear for me and what comes along with it. The naming of variables is important. By example 'costs by handling of a complaint' is misleading and should be renamed 'costs of handing complaints'. Most important if you click on the loops gnerator you only find a short loop that describes a model with nearly no dynamic at all. When one looks at the problem in general, it seems obvious that there should be some loops involving the number of customer complaints and the customer value whatever is the customer value description.
It is here that one sees the utility of a clear and complete description with words of the problem and one or two more or less higher level description diagram to help clarify the problem in question.
It would be too of extreme utility to build reality checks of the problem that would highly influence the credibility of your model (and your grading!) if it has to be presented to your examinators.
Regards.
JJ