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error in a system of equations
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Joined: 29/10/2019(UTC) Posts: 35 Location: Italy
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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
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Joined: 23/12/2011(UTC) Posts: 318 Location: italy Was thanked: 109 time(s) in 93 post(s)
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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
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Joined: 29/10/2019(UTC) Posts: 35 Location: Italy
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I tried another function but it still gives me an error...
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Joined: 04/07/2015(UTC) Posts: 6,868 Was thanked: 980 time(s) in 808 post(s)
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Originally Posted by: Ale16595 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.
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Rank: Advanced Member Groups: Registered
Joined: 29/10/2019(UTC) Posts: 35 Location: Italy
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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
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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. |
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1 user thanked mkraska for this useful post.
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Originally Posted by: Ale16595 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.
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Rank: Advanced Member Groups: Registered
Joined: 29/10/2019(UTC) Posts: 35 Location: Italy
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I tried to use the solve function but it still gives me an error saying that S is not defined
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Originally Posted by: Ale16595 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 ?
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Originally Posted by: Jean Giraud Originally Posted by: Ale16595 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
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Joined: 28/08/2014(UTC) Posts: 1,356 Was thanked: 815 time(s) in 516 post(s)
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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.
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Rank: Advanced Member Groups: Registered
Joined: 29/10/2019(UTC) Posts: 35 Location: Italy
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Originally Posted by: Razonar 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.
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Originally Posted by: Razonar 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).
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1 user thanked Jean Giraud for this useful post.
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Joined: 28/08/2014(UTC) Posts: 1,356 Was thanked: 815 time(s) in 516 post(s)
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Originally Posted by: Jean Giraud Originally Posted by: Razonar 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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