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

"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

I tried another function but it still gives me an error...

Wrote

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.

here is the spreadsheet
calcoli.sm (46,18 KiB) scaricato 1172 volta(e).
it is a system of equations derived from the condition of dynamic equilibrium in the stationary curve motion of a bicycle

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.

Wrote

here is the spreadsheet

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

calcoli.sm (52,58 KiB) scaricato 1123 volta(e).

You must make the system consitant before attempting solve.

I tried to use the solve function but it still gives me an error saying that S is not defined

Wrote

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 ?

Wrote

Wrote

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

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 (50,31 KiB) scaricato 1170 volta(e).

Best regards.
Alvaro.

Wrote

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 (50,31 KiB) scaricato 1170 volta(e).

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.

Wrote

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 (38,81 KiB) scaricato 1153 volta(e).

Wrote

Wrote

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 (38,81 KiB) scaricato 1153 volta(e).

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