Need help with formulas
Need help with formulas
Hi all,
I need help with my formulas..
@Tony: I have tried really hard to solve some formula problems but still there are some issues in the model..
I never failed in programming assignments but I see a failure coming for me in SD.
I really need help..
Thanks
Liizz
I need help with my formulas..
@Tony: I have tried really hard to solve some formula problems but still there are some issues in the model..
I never failed in programming assignments but I see a failure coming for me in SD.
I really need help..
Thanks
Liizz
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Re: Need help with formulas
We are more than happy to help. But we will not build or debug a model for you.
You haven't said in this post what you need help with. What formula are you struggling with, and have you checked the Vensim help system? It contains many sample models.
You haven't said in this post what you need help with. What formula are you struggling with, and have you checked the Vensim help system? It contains many sample models.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
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http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
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Re: Need help with formulas
Hi,
Thanks.
Of course I never expected you to design my model. I always ask for suggestion or advice before because I do not have a strong exposure in system dynamics and at times i'm uncertain about my point.
Doing an introductory module on System Dynamics at the college will not make me a genius in the field and personally, it takes time to have a system dynamic thinking.
I have written an equation for the Project perceived as completed based on Tasks Done Correctly and Scheduled Completion date.
IF THEN ELSE (Tasks Done Correctly > Initial Tasks,0,1) where Initial Tasks is 2000.
But since the project is not yet finished, I am unable to increase workforce.
Formula : Extra Personnel Needed=
MAX(MIN(Max Hires,Required workforce)-Cumulative Workforce Level,0)
Thanks
Liizz
Thanks.
Of course I never expected you to design my model. I always ask for suggestion or advice before because I do not have a strong exposure in system dynamics and at times i'm uncertain about my point.
Doing an introductory module on System Dynamics at the college will not make me a genius in the field and personally, it takes time to have a system dynamic thinking.
I have written an equation for the Project perceived as completed based on Tasks Done Correctly and Scheduled Completion date.
IF THEN ELSE (Tasks Done Correctly > Initial Tasks,0,1) where Initial Tasks is 2000.
But since the project is not yet finished, I am unable to increase workforce.
Formula : Extra Personnel Needed=
MAX(MIN(Max Hires,Required workforce)-Cumulative Workforce Level,0)
Thanks
Liizz
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Re: Need help with formulas
Hiliizz wrote:Hi,
Thanks.
Of course I never expected you to design my model. I always ask for suggestion or advice before because I do not have a strong exposure in system dynamics and at times i'm uncertain about my point.
Doing an introductory module on System Dynamics at the college will not make me a genius in the field and personally, it takes time to have a system dynamic thinking.
I have written an equation for the Project perceived as completed based on Tasks Done Correctly and Scheduled Completion date.
IF THEN ELSE (Tasks Done Correctly > Initial Tasks,0,1) where Initial Tasks is 2000.
But since the project is not yet finished, I am unable to increase workforce.
Formula : Extra Personnel Needed=
MAX(MIN(Max Hires,Required workforce)-Cumulative Workforce Level,0)
Thanks
Liizz
in your post you mention some strange variables (such as Scheduled Completion date and those in MAX(MIN...))) and moreover you do not say anything about the reasons why your IF statement gives you troubles....
Cheers
Lorenzo
Re: Need help with formulas
Tony, is there an e-mail address where I can send you my model.
Thanks
Liizz
Thanks
Liizz
Re: Need help with formulas
Please find model
Last edited by liizz on Wed Aug 27, 2014 1:01 pm, edited 1 time in total.
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Re: Need help with formulas
Why? You need to spend the time and look at the model and trace back the reason why you cannot increase the workforce. Is it because of input data? Or an incorrect equation somewhere?liizz wrote:But since the project is not yet finished, I am unable to increase workforce.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
Re: Need help with formulas
Yes.. Thanks for the help.
Re: Need help with formulas
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.
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Re: Need help with formulas
Hi,
What you mean by isolating? Should i start one afresh?
Thanks
Liizz
What you mean by isolating? Should i start one afresh?
Thanks
Liizz
Re: Need help with formulas
Tom,
Is it possible to get some discussion with you? I must say that I was able to start my model thanks 2 you as it makes me see things differently.
Thanks
Liizz
Is it possible to get some discussion with you? I must say that I was able to start my model thanks 2 you as it makes me see things differently.
Thanks
Liizz
Re: Need help with formulas
Infact, I started designing my module one by one. But when I integrate it, big issues coming out
Thanks
Liizz
Thanks
Liizz
Re: Need help with formulas
There are two ways to isolate:
- copy/paste the structure into a separate model, improve it until you are satisfied, then copy/paste back into the complete model, or
- break the causal links between the elements of the integrated model temporarily
One way to implement the second approach might be:
- copy/paste the structure into a separate model, improve it until you are satisfied, then copy/paste back into the complete model, or
- break the causal links between the elements of the integrated model temporarily
One way to implement the second approach might be:
Code: Select all
{personnel sector}
staff = INTEG( hiring-firing, initial staff )
{task sector}
work accomplished = effective staff*productivity
effective staff = IF THEN ELSE( staff test input, constant staff, staff )
constant staff = 10
staff test input = 0 or 1
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Re: Need help with formulas
Hi all,
The hiring process is working well in stand-alone mode but when coupled with productivity. Getting issues on that.
Am discouraged, am struggling too much on that.
Can I get some serious assistance on that plz?
The hiring process is working well in stand-alone mode but when coupled with productivity. Getting issues on that.
Am discouraged, am struggling too much on that.
Can I get some serious assistance on that plz?
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Re: Need help with formulas
You need to work out why it isn't working. Spend some time using the Vensim table tool and look at the numbers to work out why it's not doing what you want.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
Re: Need help with formulas
Tony,
I have been able to troubleshoot some errors up till now but this one is taking too much time.
I am making use of graphs itself. [Please see file]
The logic of the equation for the hiring process is looking fine.
My equation for : Effect of experience on productivity=
IF THEN ELSE(Cumulative Workforce Level > 0,(New Personnel*Normal productivity of new personnel
+Experienced Personnel)/Cumulative Workforce Level,1)
Thanks to advise
Liizz
I have been able to troubleshoot some errors up till now but this one is taking too much time.
I am making use of graphs itself. [Please see file]
The logic of the equation for the hiring process is looking fine.
My equation for : Effect of experience on productivity=
IF THEN ELSE(Cumulative Workforce Level > 0,(New Personnel*Normal productivity of new personnel
+Experienced Personnel)/Cumulative Workforce Level,1)
Thanks to advise
Liizz
- Attachments
-
- experience on productivity.docx
- (41.88 KiB) Downloaded 229 times
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Re: Need help with formulas
Sometimes debugging models takes a long time. Unfortunately it is something you need to do, you cannot expect others to debug your model for you. We can help with technical problems or general approaches for small problems, but not debug a model the size of this one.liizz wrote:I have been able to troubleshoot some errors up till now but this one is taking too much time.
Use the table tool.I am making use of graphs itself.
What do you need advice with?The logic of the equation for the hiring process is looking fine.
My equation for : Effect of experience on productivity=
IF THEN ELSE(Cumulative Workforce Level > 0,(New Personnel*Normal productivity of new personnel
+Experienced Personnel)/Cumulative Workforce Level,1)
Thanks to advise
Liizz
Looking at the graphs in the file, what does "effect of experience on productivity" actually mean? If it means as experience rises, productivity rises, then you model logic must be incorrect as the line is decreasing.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
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- Super Administrator
- Posts: 4613
- Joined: Wed Mar 05, 2003 3:10 am
Re: Need help with formulas
Sometimes debugging models takes a long time. Unfortunately it is something you need to do, you cannot expect others to debug your model for you. We can help with technical problems or general approaches for small problems, but not debug a model the size of this one.liizz wrote:I have been able to troubleshoot some errors up till now but this one is taking too much time.
Use the table tool as well. When debugging models, you need to look at values as well as graphs to check it is doing what you expect it to.I am making use of graphs itself.
What do you need advice with?The logic of the equation for the hiring process is looking fine.
My equation for : Effect of experience on productivity=
IF THEN ELSE(Cumulative Workforce Level > 0,(New Personnel*Normal productivity of new personnel
+Experienced Personnel)/Cumulative Workforce Level,1)
Thanks to advise
Liizz
Looking at the graphs in the file, what does "effect of experience on productivity" actually mean? If it means as experience rises, productivity rises, then you model logic must be incorrect as the line is decreasing.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
Re: Need help with formulas
Effect of experience on productivity is based on the no. of either experienced or inexperienced personnel I have?
Lets say I have 10 inexperienced, the graph shall show a decline and for experienced people it shall be a rise.
Can I send u a simplified version of it?
Thanks
Liizz
Lets say I have 10 inexperienced, the graph shall show a decline and for experienced people it shall be a rise.
Can I send u a simplified version of it?
Thanks
Liizz
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Re: Need help with formulas
Is that what happens in your model? Put 10 inexperienced people in and see what happens. Part of model building is experimenting yourself to determine if your model is behaving correctly. This is something you need to do yourself, or discuss with your tutor.liizz wrote:Lets say I have 10 inexperienced, the graph shall show a decline and for experienced people it shall be a rise.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
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Units are important!
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Re: Need help with formulas
Yes as per the graph i sent you, for inexperienced its declining.
But for experienced, it is below 2 and is going nearly constant.
haha, my tutor has no experience in modelling and no discussion
Thanks
Liizz
But for experienced, it is below 2 and is going nearly constant.
haha, my tutor has no experience in modelling and no discussion
Thanks
Liizz
Re: Need help with formulas
Plz can I send u a simplified version of my model?
Thanks
Liizz
Thanks
Liizz
Re: Need help with formulas
Kindly find the model.
Thanks
Liizz
Thanks
Liizz
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- Project Modelwith experience and productivity.mdl
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Re: Need help with formulas
Have you traced through why these values are being calculated?liizz wrote:Yes as per the graph i sent you, for inexperienced its declining.
But for experienced, it is below 2 and is going nearly constant.
haha, my tutor has no experience in modelling and no discussion
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
Re: Need help with formulas
Take a look at http://vensim.com/causal-tracing-in-vensim/, then revisit your model.
The aggregate behavior looks pretty reasonable to me, as long as willingness to increase workforce = 1. There's some steady state error (equilibrium workforce is short .3 people), because the hiring decision doesn't anticipate personnel leaving. That could be realistic, or you could add a term to the hiring rate to account for it.
The distribution of staff between inexperienced and experienced seems incorrect. If the learning and retention delays are both 10 months, you'd expect both stocks to have about the same number of people in them. I think this relates to the lookup used, which is not serving the purpose that I would guess is intended (arrival distribution for experience). Get rid of the lookup and use the standard stock/delay formulation for the assimilation rate and it should work fine.
The aggregate behavior looks pretty reasonable to me, as long as willingness to increase workforce = 1. There's some steady state error (equilibrium workforce is short .3 people), because the hiring decision doesn't anticipate personnel leaving. That could be realistic, or you could add a term to the hiring rate to account for it.
The distribution of staff between inexperienced and experienced seems incorrect. If the learning and retention delays are both 10 months, you'd expect both stocks to have about the same number of people in them. I think this relates to the lookup used, which is not serving the purpose that I would guess is intended (arrival distribution for experience). Get rid of the lookup and use the standard stock/delay formulation for the assimilation rate and it should work fine.
/*
Advice to posters (it really helps us to help you)
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Blog: http://blog.metasd.com
Model library: http://models.metasd.com
Bookmarks: http://delicious.com/tomfid/SystemDynamics
*/
Advice to posters (it really helps us to help you)
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Bookmarks: http://delicious.com/tomfid/SystemDynamics
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