Hi all,
I was working on eviews on a macroeconomic model. The model is a system of simultaneous equations, which I think Vensim will be great to work on the simulations. However, the model has the following properties for many variables:
1. k_k(t) = k_k(t-1)*(1 + gr_k(t))
2. gr_k(t) = gamma0 + gammau*u(t-1) - gammar*rr_l(t)
3. u(t) = y_k(t)/k_k(t-1)
....etc.
most variables will have an initial value to start with
I wonder how to make such simulations possible ... Thank you for the help!
Help: time series data with time lags
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Re: Help: time series data with time lags
This question is far too vague to really provide an answer. What do these equations even mean?
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Re: Help: time series data with time lags
Hi there, thank you for the reply. I only took a few equations out of the system, as I don't know how to include lagged variables in a vensim model. However, to explain what the equations are:
1. capital stock grows at a rate of gr_k, hence at time t, k_k(t)= k_k(t-1)*(1+gr_k)
2. the growth rate is defined by a the following equations all gammas are parameters (constants)
e.g. gr_k=1+2*u(t-1)-3*rr_l (t), where u is the capital utilization proxy and rr_l is the real lending rate
3. u = y_k(t)/k_k(t-1) is showing that capital utilization proxy is the ratio between current real GDP flow and the real capital stock from last year
and there are many other simultaneous equations with lagged variables in the whole system.
If you could share an example vensim file for maybe just one of the equations, that'd be very helpful!
1. capital stock grows at a rate of gr_k, hence at time t, k_k(t)= k_k(t-1)*(1+gr_k)
2. the growth rate is defined by a the following equations all gammas are parameters (constants)
e.g. gr_k=1+2*u(t-1)-3*rr_l (t), where u is the capital utilization proxy and rr_l is the real lending rate
3. u = y_k(t)/k_k(t-1) is showing that capital utilization proxy is the ratio between current real GDP flow and the real capital stock from last year
and there are many other simultaneous equations with lagged variables in the whole system.
If you could share an example vensim file for maybe just one of the equations, that'd be very helpful!
Re: Help: time series data with time lags
Hi, thank you for the reply. I only took a few equations out of the system, as I don't know how to include lagged variables in a vensim model. However, to explain what the equations are:Administrator wrote: ↑Mon Jun 04, 2018 6:03 pm This question is far too vague to really provide an answer. What do these equations even mean?
1. capital stock grows at a rate of gr_k, hence at time t, k_k(t)= k_k(t-1)*(1+gr_k)
2. the growth rate is defined by a the following equations all gammas are parameters (constants)
e.g. gr_k=1+2*u(t-1)-3*rr_l (t), where u is the capital utilization proxy and rr_l is the real lending rate
3. u = y_k(t)/k_k(t-1) is showing that capital utilization proxy is the ratio between current real GDP flow and the real capital stock from last year
and there are many other simultaneous equations with lagged variables in the whole system.
If you could share an example vensim file for maybe just one of the equations, that'd be very helpful!
-
- Super Administrator
- Posts: 4573
- Joined: Wed Mar 05, 2003 3:10 am
Re: Help: time series data with time lags
I think it's probably best if you have a go first and upload the model if you have any problem.
Things like k_k(t-1) is not the right way to think about it when building a model. Vensim steps forwards in "time step" increments, so t-1 can mean today - 1 (yesterday), this month - 1 (yesterday or last month?). What does t-1 actually mean, is it last month, last week, the last time the simlation stepped forward etc.
Things like k_k(t-1) is not the right way to think about it when building a model. Vensim steps forwards in "time step" increments, so t-1 can mean today - 1 (yesterday), this month - 1 (yesterday or last month?). What does t-1 actually mean, is it last month, last week, the last time the simlation stepped forward etc.
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: Help: time series data with time lags
all data are annual data, hence the initial value coincides with year 0 (e.g. 1950) k_k(1951)=k_k(1950)*(1+growth rate). Hope this time is clearerAdministrator wrote: ↑Mon Jun 04, 2018 7:05 pm I think it's probably best if you have a go first and upload the model if you have any problem.
Things like k_k(t-1) is not the right way to think about it when building a model. Vensim steps forwards in "time step" increments, so t-1 can mean today - 1 (yesterday), this month - 1 (yesterday or last month?). What does t-1 actually mean, is it last month, last week, the last time the simlation stepped forward etc.
Re: Help: time series data with time lags
This explains the mapping between discrete and continuous time, and why discrete notation for continuous phenomena is usually problematic:
http://metasd.com/2017/11/discrete-time-stinks/
http://metasd.com/2017/11/discrete-time-stinks/
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Blog: http://blog.metasd.com
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Re: Help: time series data with time lags
Thank you, will have a looktomfid wrote: ↑Tue Jun 05, 2018 12:35 pm This explains the mapping between discrete and continuous time, and why discrete notation for continuous phenomena is usually problematic:
http://metasd.com/2017/11/discrete-time-stinks/