different result

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depe76
Junior Member
Posts: 2
Joined: Wed Sep 29, 2021 7:24 am
Vensim version: PLE

different result

Post by depe76 »

dear forum,
i intend to calculate investment model (to find out investment period and NPV) and I made a submodel like the attached one. But surprisingly the result was different from manual calculation using Excel.
Can anybody help telling me what went wrong with my model?
Thanks and regards
screen shot sub model.jpg
screen shot sub model.jpg (122.5 KiB) Viewed 1869 times
comparison.jpg
comparison.jpg (412.51 KiB) Viewed 1869 times
Administrator
Super Administrator
Posts: 4573
Joined: Wed Mar 05, 2003 3:10 am

Re: different result

Post by Administrator »

It's impossible to help with just screen shots.

Have you reviewed the documentation for the NPV/NPVE functions?

http://www.vensim.com/documentation/fn_npv.html
http://www.vensim.com/documentation/fn_npve.html
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
depe76
Junior Member
Posts: 2
Joined: Wed Sep 29, 2021 7:24 am
Vensim version: PLE

Re: different result

Post by depe76 »

sorry I forgot to attach the model
experiment simulasi.mdl
(2.16 KiB) Downloaded 145 times
Administrator
Super Administrator
Posts: 4573
Joined: Wed Mar 05, 2003 3:10 am

Re: different result

Post by Administrator »

Still not possible to help you. You haven't provided the spreadsheet so we can see the calculations or instructions on what to look at.

I'd suggest making sure the model passes the units check before you start comparing it with other calculations.

My guess is that the equation for "harga sewa" is incorrect. You are accumulating the rate plus the level itself. This is similar to

x(t) = x(t-1) + x(t-1) + rate
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
tomfid
Administrator
Posts: 3806
Joined: Wed May 24, 2006 4:54 am

Re: different result

Post by tomfid »

I think the key problem here is indeed the equation for harga sewa. Currently it is:

INTEG( rate harga sewa+harga sewa, 25000)

but it probably should be

INTEG( rate harga sewa, 25000)

Units checking would reveal the error, if units were defined.
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