Search found 105 matches

by WayneZhou2009
Thu Apr 19, 2018 7:39 pm
Forum: Vensim
Topic: Potential doublecounting in a example model
Replies: 8
Views: 4553

Re: Potential doublecounting in a example model

Hi Tom, Thanks for your further comments. Did you mean to apply SMOOTH to demolition replacement, but NOT to the gap in house? But, in reality, as you said, the market only responds when the gap has grown big enough. It has to take enough time for the gap to grow and thus be perceived by the market....
by WayneZhou2009
Thu Apr 19, 2018 7:35 pm
Forum: Vensim
Topic: Potential doublecounting in a example model
Replies: 8
Views: 4553

Re: Potential doublecounting in a example model

Hi JJ, Thanks for your insights. If my understanding of what you said is correct, did you suggest to apply SMOOTH to demolition replacement, with around 1 year time to perceive (slightly more than 10 months), AND at the same time also apply SMOOTH to the gap in house (number of houses required - Hou...
by WayneZhou2009
Thu Apr 19, 2018 5:38 pm
Forum: Vensim
Topic: How to set "bidirectional" flow for a stock
Replies: 3
Views: 2318

Re: How to set "bidirectional" flow for a stock

Thanks a lot, Tom.

So there is no need to explicitly showing two arrows for one flow, i.e. one arrow of the flow going into the stock and the other arrow going into the cloud? Or maybe this is simply not realisable graphically?
by WayneZhou2009
Thu Apr 19, 2018 5:14 pm
Forum: Vensim
Topic: How to set "bidirectional" flow for a stock
Replies: 3
Views: 2318

How to set "bidirectional" flow for a stock

Hi,
For a stock with just one flow, how to set the flow to be "bidirectional", so that the flow can sometimes be an inflow and sometimes be an outflow of the stock, depending upon the stock level as compared with an exogenously changing target?

Many thanks.
by WayneZhou2009
Thu Apr 19, 2018 4:32 pm
Forum: Vensim
Topic: Potential doublecounting in a example model
Replies: 8
Views: 4553

Potential doublecounting in a example model

Hi, This might be trivial to ask, but somehow I could not figure it out. It is about a sample in Vensim's UserGuide Chap11 folder, Houses.mdl. The "planning" rate is defined to be MAX( 0, replacement houses + (gap in houses / time to respond to gap)), the "gap in houses" is defin...
by WayneZhou2009
Mon Mar 05, 2018 3:50 pm
Forum: Vensim
Topic: Defining ppriority and pwidth of ALLOCATE AVAILABLE function
Replies: 4
Views: 2762

Re: Defining ppriority and pwidth of ALLOCATE AVAILABLE function

Hi Tomfid / Administrator, I am not sure if you have got a chance to read my questions above, but I would be very grateful if you could offer some comments/advices. A related question is that: suppose cost is the only criterion to determine priority of plants, but for each plant type, the cost is a ...
by WayneZhou2009
Thu Mar 01, 2018 2:38 pm
Forum: Vensim
Topic: Defining ppriority and pwidth of ALLOCATE AVAILABLE function
Replies: 4
Views: 2762

Re: Defining ppriority and pwidth of ALLOCATE AVAILABLE function

Hi Tomfid, Many thanks for your reply. Yes, the plant efficiency is of concern because of emissions. So, if I understand your suggested approach correctly, that would lead to a combined "ppriority" under priority profile of the ALLOCATE AVAILABLE function which is sort of "fixed"...
by WayneZhou2009
Thu Mar 01, 2018 11:53 am
Forum: Vensim
Topic: Defining ppriority and pwidth of ALLOCATE AVAILABLE function
Replies: 4
Views: 2762

Defining ppriority and pwidth of ALLOCATE AVAILABLE function

Hi Tomfid and Administrator, I have a question about defining the ppriority and pwidth of the ALLOCATE AVAILABLE function. Suppose I have 2 types of power plants to construct to meet an increasing power demand (exogenous). - For Plant A, its average capital cost is 1000 USD/KW and standard deviation...
by WayneZhou2009
Tue Feb 20, 2018 10:29 am
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Sorry, I meant "VECTOR LOOKUP". It was a typo. Hi Tom, just a further question following my post above. (4) As you pointed out, whilst the results of the closed-loop approach are very similar to using VECTOR LOOP, it is not cost minimizing, strictly speaking. So, is there a way to extend t...
by WayneZhou2009
Tue Feb 20, 2018 10:27 am
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Hi Tom, just a further question following my post above. (4) As you pointed out, whilst the results of the closed-loop approach are very similar to using VECTOR LOOP, it is not cost minimizing, strictly speaking. So, is there a way to extend the current closed-loop approach to realise cost minimizin...
by WayneZhou2009
Tue Feb 20, 2018 10:21 am
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Hi Tom, Many thanks for your model, which is enlightening. Having studied it carefully, I still have a couple of questions and would be very grateful if you could offer some further guidance. (1) The priority of each car type as a function of price and fuel economy is very sensible. But how to assig...
by WayneZhou2009
Mon Feb 19, 2018 1:33 pm
Forum: Vensim
Topic: How to edit/delete own posts and attachments?
Replies: 3
Views: 2101

Re: How to edit/delete own posts and attachments?

Thanks Administrator for your clarification. How about attachments in old posts by oneself? You can no longer delete your old posts (someone did this which made the replies seem like nonsense). You should be able to edit them though. But please only edit if you are adding information. The forum exis...
by WayneZhou2009
Mon Feb 19, 2018 1:16 pm
Forum: Vensim
Topic: How to edit/delete own posts and attachments?
Replies: 3
Views: 2101

How to edit/delete own posts and attachments?

Hi administrators,

I have a general question about how to edit or delete old posts (and attachments) of my own. Somehow I cannot find how I can do it, although I remember there was such function enabled by the forum in the past. Please could you advise?

Many thanks.
by WayneZhou2009
Mon Feb 12, 2018 7:57 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Hi Tom, please may I follow up with you on your thoughts about my questions in my original post above? Your help is greatly appreciated. Here are some other open loop approaches: http://metasd.com/2018/02/polynomials-interpolating-functions-decision-rules/ Since you're already using VECTOR LOOKUP, t...
by WayneZhou2009
Fri Feb 09, 2018 12:12 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Thanks a lot Tom. Looking forward very much to more thoughts from you. Many thanks.
tomfid wrote:Here are some other open loop approaches:
http://metasd.com/2018/02/polynomials-i ... ion-rules/
Since you're already using VECTOR LOOKUP, this is probably not needed.

More thoughts later.
by WayneZhou2009
Wed Feb 07, 2018 5:56 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Attachments are files for approach 2.
by WayneZhou2009
Wed Feb 07, 2018 5:55 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 7345

Optimization - VECTOR LOOKUP and other approaches ?)

Hello, I am working on a model which is about the average fuel economy (liter/kilometer) of cars in a stock of cars. The stock has a desired stock level (exogenous). There are 3 types of car representing different combination of price (exogenous) and fuel economy levels (exogenous). Every year, 3 ty...
by WayneZhou2009
Tue Dec 12, 2017 6:53 pm
Forum: Vensim
Topic: Secondary Y axis in custom graph
Replies: 5
Views: 2943

Re: Secondary Y axis in custom graph

Thanks Tom. So there is no way to have two scales, with one on the left and the other one on the right, just like what can be easily realised in Excel? You can have 2 scales, but they appear together on the left. They're useful for a modeler who knows what's going on, but I wouldn't recommend it for...
by WayneZhou2009
Sun Dec 03, 2017 2:27 pm
Forum: Vensim
Topic: How to set extremely low stock to be exactly zero and ensure reasonable co-flow results?
Replies: 1
Views: 1506

How to set extremely low stock to be exactly zero and ensure reasonable co-flow results?

Hi, Sometimes a stock reaches extremely low level. For example, it remains positive but is as low as something like 3e-12. This might not be a critical issue when only the stock is of interest. However, when a coflow is involved in the model and the stock level is used as the denominator in the calc...
by WayneZhou2009
Sat Dec 02, 2017 11:05 pm
Forum: Vensim
Topic: Cap for multiple outflows to avoid negative stock
Replies: 2
Views: 2081

Cap for multiple outflows to avoid negative stock

Hi, With regard to the method to avoid negative stock, a common practice is to set a cap for the outflow as suggested by previous posts, i.e. outflow = MIN (desired outflow, stock/minimum time to drain stock) This is a very useful method. But how about a stock having multiple outflows? How should th...
by WayneZhou2009
Fri Dec 01, 2017 12:36 pm
Forum: Vensim
Topic: Secondary Y axis in custom graph
Replies: 5
Views: 2943

Re: Secondary Y axis in custom graph

Hi thanks for reply. However I do not think it answers my real question which is regarding the creation of a secondary Y axis on a customized graph? If you already have your custom graph created, yes. Insert an IO object, and select "Output custom graph". Then select the graph from the dro...
by WayneZhou2009
Fri Dec 01, 2017 11:12 am
Forum: Vensim
Topic: Secondary Y axis in custom graph
Replies: 5
Views: 2943

Secondary Y axis in custom graph

Hi,

Just a small question about graph display - would it be possible to have a secondary Y axis (on the right side) in a customized graph which is embedded in a model as an I/O object?

I've done some searching in the forum but failed to find the answer. Thank you so much.
by WayneZhou2009
Tue Nov 28, 2017 11:26 pm
Forum: Vensim
Topic: Limit of number of variables included in a custom graph
Replies: 2
Views: 1737

Re: Limit of number of variables included in a custom graph

Thank you so much Tom. It worked perfectly.
tomfid wrote:You can put more than 6 if you export the graph set to .vgd and edit it with a text editor, I think.
by WayneZhou2009
Tue Nov 28, 2017 10:09 pm
Forum: Vensim
Topic: Limit of number of variables included in a custom graph
Replies: 2
Views: 1737

Limit of number of variables included in a custom graph

Hi, This may seems to trivial to ask, but I have just come across this issue: When producing custom graphs through the "Graphs" tab of the Control Panel, there is a limit of up to 6 variables that can be included in a single graph (6 lines under "Variable" of the dialog window af...
by WayneZhou2009
Fri Nov 24, 2017 10:17 am
Forum: Vensim
Topic: Model changing lifetime due to renovation
Replies: 30
Views: 13345

Re: Model changing lifetime due to renovation

Hi JJ, thank you so much for your further comments. All very much appreciated. As I said before, this is for my own exercise only, nothing to do with consultancy or something else. I do agree with you that models shall be made simpler as far as possible. Your comments on the efficiency are all corre...