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Offline Ale16595  
#1 Posted : 05 November 2019 20:02:37(UTC)
Ale16595


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Hi to everyone
I am having difficulty solving a linear system like in the picture.
the error says:"impossible to get or set an item because it does not exist"
does anyone know where the error can be and how to solve this problem?
Thanks in advance
ferrvrveve.png

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Offline PompelmoTell  
#2 Posted : 05 November 2019 21:08:12(UTC)
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"roots" does not work with the units. You must adimensionare equations, or you can try the other features present in the plugin (eg "FindRoot" present "Nonlinear solvers" plugin)

sergio
Offline Ale16595  
#3 Posted : 05 November 2019 21:52:23(UTC)
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I tried another function but it still gives me an error...
oioijoijoijoi.png
Offline Jean Giraud  
#4 Posted : 06 November 2019 05:57:28(UTC)
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Originally Posted by: Ale16595 Go to Quoted Post
I tried another function but it still gives me an error...

It's a huge system, and generally does not accept all initials same.
I would zap units first. This kind of solving should have it be
solved from P & P [Pain & Prestige] as it reflects real project
that does come out of the blue. Even Mathcad Given/Find may fail
or pedal through constrain.
Attach the work sheet ... some source reference as well.

Offline Ale16595  
#5 Posted : 06 November 2019 08:25:20(UTC)
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here is the spreadsheet
calcoli.sm (47kb) downloaded 19 time(s).
it is a system of equations derived from the condition of dynamic equilibrium in the stationary curve motion of a bicycle
Offline mkraska  
#6 Posted : 06 November 2019 10:16:32(UTC)
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Equations 3 and 4 probably demand different values for N.r+N.f So there is no solution.

If the system has a solution, the function Solve() from Maxima plugin might find it.

2019-11-06 08_14_22-SMath Studio - [calcoli.sm_].png
Martin Kraska

Pre-configured portable distribution of SMath Studio: https://smath.com/wiki/SMath_with_Plugins.ashx
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on 06/11/2019(UTC)
Offline Jean Giraud  
#7 Posted : 06 November 2019 21:20:34(UTC)
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Originally Posted by: Ale16595 Go to Quoted Post
here is the spreadsheet

1. equalities [1,2,3] are consistant 'N'
2. equalities [4,5,6] are inconsistant 'mixed units'

calcoli.sm (53kb) downloaded 17 time(s).

You must make the system consitant before attempting solve.
Offline Ale16595  
#8 Posted : 06 November 2019 21:35:50(UTC)
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I tried to use the solve function but it still gives me an error saying that S is not defined
hfhfhfhfhffhfh.png
Offline Jean Giraud  
#9 Posted : 06 November 2019 21:47:31(UTC)
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Originally Posted by: Ale16595 Go to Quoted Post
I tried to use the solve function but it still gives me an error saying that S is not defined

Did you read my reply just before your visit ?
Offline Ale16595  
#10 Posted : 06 November 2019 22:20:21(UTC)
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Originally Posted by: Jean Giraud Go to Quoted Post
Originally Posted by: Ale16595 Go to Quoted Post
I tried to use the solve function but it still gives me an error saying that S is not defined

Did you read my reply just before your visit ?


sorry, when I wrote, I didn't notice your message
Offline Razonar  
#11 Posted : 11 November 2019 05:11:18(UTC)
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Hi. Try this setup, using al_ library. I don't know if using better guess values can get better results (eqn 3 and 4 don't get good results)

calcoli.sm (51kb) downloaded 21 time(s).

Best regards.
Alvaro.
Offline Ale16595  
#12 Posted : 11 November 2019 13:37:20(UTC)
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Originally Posted by: Razonar Go to Quoted Post
Hi. Try this setup, using al_ library. I don't know if using better guess values can get better results (eqn 3 and 4 don't get good results)

calcoli.sm (51kb) downloaded 21 time(s).

Best regards.
Alvaro.


Hi, thanks for the reply, but I think I found the error. The system I wrote has two linearly dependent equations, and for this reason it cannot find a solution.
I will have to modify the whole problem.
Offline Jean Giraud  
#13 Posted : 11 November 2019 20:55:47(UTC)
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Originally Posted by: Razonar Go to Quoted Post
Hi. Try this setup, using al_ library. I don't know if using better guess values can get better results (eqn 3 and 4 don't get good results)

Hello Alvaro,
The attached CSTR [SS 6179] example is offered differently,
it is initialized from random guesses: success.
Cheers ... Jean

Solve al_nleqsolve CSTR.sm (39kb) downloaded 32 time(s).

thanks 1 user thanked Jean Giraud for this useful post.
on 12/11/2019(UTC)
Offline Razonar  
#14 Posted : 12 November 2019 19:29:59(UTC)
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Originally Posted by: Jean Giraud Go to Quoted Post
Originally Posted by: Razonar Go to Quoted Post
Hi. Try this setup, using al_ library. I don't know if using better guess values can get better results (eqn 3 and 4 don't get good results)

Hello Alvaro,
The attached CSTR [SS 6179] example is offered differently,
it is initialized from random guesses: success.
Cheers ... Jean

Solve al_nleqsolve CSTR.sm (39kb) downloaded 32 time(s).



Hi Jean. Thanks, very interesting.
Best regards.
Alvaro.
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