Search found 3806 matches
- Fri Jan 27, 2017 6:06 pm
- Forum: Ventity
- Topic: Mortality rates in a cohort model depending on creation time of the cohort
- Replies: 28
- Views: 60739
Re: Mortality rates in a cohort model depending on creation time of the cohort
I made a few mods, partly cleanup, but mainly to implement the switchover from cohort-specific mortality tables to a group generic mortality table. CohortPopGroups3 Test Swiss Population V2.zip That creates discontinuities in the mortality rate for each cohort, which seems problematic. It might be b...
- Fri Jan 27, 2017 3:28 pm
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
Not at all dumb/boring. I can think of two ways to do a Monte Carlo with a lognormal distribution. Assuming your equation is: z = EXP( mean_ln_x + RANDOM NORMAL( -6,6,0,stdev_ln_x,seed )) 1. You can make the seed parameter a VECTOR input in the sensitivity setup. Or, use a seed of 0 and vary the NOI...
- Thu Jan 26, 2017 6:43 pm
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
If the actual distribution of the data is lognormal, it seems odd to work with the ordinary mean and variance, rather than the geometric mean and variance. Be that as it may ... geometric mean = ln( arithmetic mean / sqrt( 1 + arithmetic variance / arithmetic mean^2 ) ) geometric std dev = sqrt( ln(...
- Mon Jan 23, 2017 6:07 pm
- Forum: Vensim
- Topic: Tutorials (Video + text)
- Replies: 19
- Views: 43430
Re: Tutorials (Video + text)
There's a new series on discrete and stochastic events at
http://vensim.com/discrete-stochastic/
http://vensim.com/discrete-stochastic/
- Mon Jan 23, 2017 6:02 pm
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
Oops! I goofed.
You want
z = EXP( mean_ln_x + RANDOM NORMAL( -6,6,0,stdev_ln_x,seed ))
or
z = geometric mean * EXP( RANDOM NORMAL( -6,6,0,stdev_ln_x,seed ))
You want
z = EXP( mean_ln_x + RANDOM NORMAL( -6,6,0,stdev_ln_x,seed ))
or
z = geometric mean * EXP( RANDOM NORMAL( -6,6,0,stdev_ln_x,seed ))
- Mon Jan 23, 2017 5:59 pm
- Forum: Vensim
- Topic: Somebody help me please!! ramp and pulse train combination
- Replies: 33
- Views: 14487
Re: Somebody help me please!! ramp and pulse train combination
The MODULO function is simpler - you might try it.
You can pass the sawtooth from MODULO through a lookup if you want to get a complex shape for the pulse train.
I think if we knew what you were doing, we could make better suggestions.
You can pass the sawtooth from MODULO through a lookup if you want to get a complex shape for the pulse train.
I think if we knew what you were doing, we could make better suggestions.
- Mon Jan 23, 2017 5:46 pm
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
Suppose you have data x= 10 100 1000 Compute y = ln(x) = 2.3 4.6 6.9 Mean(ln(x)) = 4.6 and stdev(ln(x))=1.88. Note that exp(4.6)=100, as you'd hope. Then you can generate a sample via: z = mean_ln_x * EXP( RANDOM NORMAL( -6,6,0,stdev_ln_x,seed )) You can do all this in Excel using the average() and ...
- Fri Jan 20, 2017 7:40 pm
- Forum: Vensim
- Topic: difficulty to download models from the models library
- Replies: 9
- Views: 5279
Re: difficulty to download models from the models library
It worked, but it was in my spam queue. Not sure why.
- Fri Jan 20, 2017 7:07 pm
- Forum: Vensim
- Topic: difficulty to download models from the models library
- Replies: 9
- Views: 5279
Re: difficulty to download models from the models library
There are no comments in my queue on metasd.com. Possibly another browser problem?
I've realized that I overused the Poisson distribution in the car model, so a new version will be arriving soon.
I've realized that I overused the Poisson distribution in the car model, so a new version will be arriving soon.
- Fri Jan 20, 2017 4:14 pm
- Forum: Vensim
- Topic: Somebody help me please!! ramp and pulse train combination
- Replies: 33
- Views: 14487
Re: Somebody help me please!! ramp and pulse train combination
1 - Every feedback loop must have a stock in it. This is not only a PLE limitation, it's also reality. A simultaneous equation loop might be a workaround for some "stiff model" situation, like a rapid market-clearing process embedded in a model with slow dynamics, but more often it's a con...
- Fri Jan 20, 2017 3:30 pm
- Forum: Vensim
- Topic: difficulty to download models from the models library
- Replies: 9
- Views: 5279
Re: difficulty to download models from the models library
Works fine for me too. I think the MIME type for mdl files is set incorrectly, but if you right-click-download them, they work fine (otherwise they open as text in the browser).
The private message system on the SD society forum doesn't seem to be working.
The private message system on the SD society forum doesn't seem to be working.
- Thu Jan 19, 2017 6:34 pm
- Forum: Ventity
- Topic: Mortality rates in a cohort model depending on creation time of the cohort
- Replies: 28
- Views: 60739
Re: Mortality rates in a cohort model depending on creation time of the cohort
That sounds sensible. The reason I'm interested in an explicit stock of health status is the following thought experiment. Suppose you have two initially identical cohorts. Cohort A starts around WWII and experiences the diet, exercise and health care that prevailed over the actual intervening decad...
- Wed Jan 18, 2017 11:43 pm
- Forum: Ventity
- Topic: Minor question for CohortPop2
- Replies: 1
- Views: 2816
Re: Minor question for CohortPop2
I don't have it running at the moment, but that message indicates that an equation uses inputs that aren't shown on the diagram. This used to happen a lot in actions because there were some loose ends in the diagramming code. You should be able to edit Parent.Head Cohort, right-click the missing cau...
- Wed Jan 18, 2017 11:41 pm
- Forum: Ventity
- Topic: Mortality rates in a cohort model depending on creation time of the cohort
- Replies: 28
- Views: 60739
Re: Mortality rates in a cohort model depending on creation time of the cohort
This is not my area, but I'd think it could get messy. Some thoughts: Frequently, models use mortality rate = f(age) implemented with a lookup. You could generalize to: mortality rate = f(age, gender, behavior, time) where the time component picks up the technical progress aspect. Substituting and e...
- Wed Jan 18, 2017 11:23 pm
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
The wikipedia article on the lognormal distribution, https://en.wikipedia.org/wiki/Log-normal_distribution , lists formulas for converting between the arithmetic and geometric means and variances. If you have a sample of data, the natural thing to do is to compute the mean(log(data)) etc. directly. ...
- Wed Jan 18, 2017 8:01 pm
- Forum: Vensim
- Topic: How to model random delay within min/max?
- Replies: 6
- Views: 3876
- Mon Jan 16, 2017 2:57 am
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
If you want x distributed lognormal, with mean(x) = 165, that's not what you have here. Your equation gives mean(log(x)) = 165. The mean of the lognormal is exp(mu + sigma^2/2), where mu and sigma are parameters of the corresponding normal. The median and geometric mean of the lognormal are exp(mu)....
- Mon Jan 16, 2017 2:31 am
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
Your formulation suggests that some quantity has a geometric mean of e^165 - what physical meaning does that have? It's more than the number of particles in the universe.
- Sun Jan 15, 2017 5:53 pm
- Forum: Vensim
- Topic: Lognormal in Vensim
- Replies: 25
- Views: 31804
Re: Lognormal in Vensim
In single precision Vensim (i.e. any version but DSS DP), taking EXP(x) with x greater than about 30 will cause an overflow. In double precision you can get to something like x ~= 300. But either way, anything that big is unlikely to be meaningful, so I'd guess you have an error. If you really have ...
- Sun Jan 15, 2017 2:04 am
- Forum: Vensim
- Topic: How to simulate a Raleigh distribution with a Weibull one
- Replies: 4
- Views: 2839
Re: How to simulate a Raleigh distribution with a Weibull one
I agree that the stretch parameter is the one to use.
For all the functions, the result is essentially
y = shift + stretch*x
where x is some kind of standard version of the distribution.
For all the functions, the result is essentially
y = shift + stretch*x
where x is some kind of standard version of the distribution.
- Tue Jan 10, 2017 3:03 pm
- Forum: Vensim
- Topic: how to set a target value for my model?
- Replies: 5
- Views: 2708
Re: how to set a target value for my model?
Assuming the latter, you could do the following: - Create a metric that is a function of the gap between your target and actual values, like error = (target-actual)^2 weight = {some negative value} - Create a payoff that minimizes the metric *p error/weight - Optimize For this to work, the model and...
- Tue Jan 10, 2017 2:22 pm
- Forum: Vensim
- Topic: how to set a target value for my model?
- Replies: 5
- Views: 2708
Re: how to set a target value for my model?
Are you looking for a dynamic target that affects the behavior of decisions, or goal-seeking optimization?
- Mon Jan 09, 2017 3:53 pm
- Forum: Vensim
- Topic: Obtain current state of intermediate steps in Dynamic functions
- Replies: 2
- Views: 2255
Re: Obtain current state of intermediate steps in Dynamic functions
Some dynamic variables are implemented as macros, and you can turn on visibility of their internals (Tools>Options>Settings). Check "Show" for "Macro Variables" (near the middle of the dialog pane). However, the discrete or infinite order delays are not among them. If you need th...
- Thu Jan 05, 2017 3:52 am
- Forum: Vensim
- Topic: Bug Report: Options Window in Model Reader v6.4E is Blank
- Replies: 3
- Views: 2228
Re: Bug Report: Options Window in Model Reader v6.4E is Blank
We won't revert. This is probably something simple. Thanks for the report.
- Fri Dec 30, 2016 3:47 pm
- Forum: Vensim
- Topic: cumulative value over specified time range
- Replies: 2
- Views: 1903
Re: cumulative value over specified time range
Something like:
Code: Select all
cumulative = INTEG( inflow, 0 ) ~ $
inflow = STEP(1,start time) * fund_flow ~ $/day
start time = 5 ~ days