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Solving equations system

mvicenzi
4-Participant

Solving equations system

According to some web tutorials, I have tried to solve the equations system you can find in the attached figure.

I want to solve the system in order to find variables x and e. All the other variables are defined (you can see defined values also for e and x, they are guess values according to tutorials).

 

I am not able to find out what is my mistake, if I click on "sol" I see the error "This variable is undefined".

 

You find also the Mathcad file attached.

 

Can someone help me?

 

Sincerely

Stefano Grandi

1 ACCEPTED SOLUTION

Accepted Solutions
JeffH1
13-Aquamarine
(To:mvicenzi)

Two issues here.  One solvable, one not.

 

Firstly, to use the Find(x) function to solve a system, you must place a Given command before your two equation constraints.

 

Secondly, before solving anything, always plot your data.  If we rearrange the first equation, putting variable e on the left side (it is separable) and call this e1(x), we can get an idea of how this equation behaves.  Rearranging the second equation in terms of e and calling this e2(x) gives a look at how both equations look and where they may intersect.

JeffH1_0-1652265030678.png

JeffH1_1-1652265081366.png

JeffH1_2-1652265134180.png

 

They do not intersect.  There is no solution.

 

View solution in original post

3 REPLIES 3

Hi,

The "Given" keyword needs to be placed after the guess values and before the equations of the solve block.

 

With the two equations as they stand Fm.c=5 and T=2000 you can set x, e to get 5 and 2000 but not with the same values.

Please check your equations.

 

Solve block works Fm.c=5 and T=2 to show you it can work if equations are solvable.

Capture.JPG

Cheers

Terry

Thank you very much @terryhendicott and @JeffH1!

I solved my issue and I will keep in mind to plot curves before.

 

Regards

JeffH1
13-Aquamarine
(To:mvicenzi)

Two issues here.  One solvable, one not.

 

Firstly, to use the Find(x) function to solve a system, you must place a Given command before your two equation constraints.

 

Secondly, before solving anything, always plot your data.  If we rearrange the first equation, putting variable e on the left side (it is separable) and call this e1(x), we can get an idea of how this equation behaves.  Rearranging the second equation in terms of e and calling this e2(x) gives a look at how both equations look and where they may intersect.

JeffH1_0-1652265030678.png

JeffH1_1-1652265081366.png

JeffH1_2-1652265134180.png

 

They do not intersect.  There is no solution.

 

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