topic Re: Solving a system of 5 equations with 7 variables in Mathcad

Solving a system of 5 equations with 7 variables

dthunes — Thu, 03 May 2018 13:57:27 GMT

I find myself constantly using a system of 5 equations with 7 different variables. I always know two of the variables, but the two that I know changes. Is there a way to write a single calculator that can solve for the unknowns instead of writing a different calculator for each combination?equations:mt=mf+mwc=mf/mtvf=mf/8.34vw=mw/8.34vt=vf+vwUsing

Re: Solving a system of 5 equations with 7 variables

LucMeekes — Thu, 29 Dec 2016 21:10:43 GMT

Something like this:

Success!

Luc

Re: Solving a system of 5 equations with 7 variables

Werner_E — Thu, 29 Dec 2016 22:12:29 GMT

You can turn Luc's solution into a function with the two conditions (the two known variable values) as arguments.

I add those equations to Luc's EQ and solve this system for all 7 variables, so you always get all 7 variables as result.

Drawback is that you have to evaluate this function symbolically.

Re: Solving a system of 5 equations with 7 variables

ValeryOchkov — Fri, 30 Dec 2016 05:14:22 GMT

2 equations, 3 unknowns - my solution

Re: Solving a system of 5 equations with 7 variables

ValeryOchkov — Fri, 30 Dec 2016 05:33:57 GMT

By help user function creating and using:

Re: Solving a system of 5 equations with 7 variables

vlehner — Fri, 30 Dec 2016 10:11:34 GMT

Valery,

Can you explain me, how your Equation System will be solved symbolical by MathCad?

I tryed to reproduce it, but it fails...

I have Prime 3.1

Can you post your sheet?

Thank you

Volker

Re: Solving a system of 5 equations with 7 variables

-MFra- — Fri, 30 Dec 2016 10:36:14 GMT

Hi David,

Here below I give you an example of how to solve a non-normal system:

Greetings FM

Re: Solving a system of 5 equations with 7 variables

Werner_E — Fri, 30 Dec 2016 10:45:33 GMT

F.M. wrote:

Hi David,

Here below I give you an example of how to solve a non-normal system:

But Davids system is not "non-normal"! He always has a system consisting of 5 equations with 5 unknowns!

Unfortunately, while the 5 equations are always the same, the 5 unknowns vary and can be any of 7 variables - 2 are always known.

As he does not want to create 21 separate solve blocks or symbolic solve statements, he was asking for a more compact solution.

Re: Solving a system of 5 equations with 7 variables

Werner_E — Fri, 30 Dec 2016 10:49:00 GMT

Guess you can find the sheet here -> Plot of a Function-vector-matrix

Re: Solving a system of 5 equations with 7 variables

LucMeekes — Fri, 30 Dec 2016 10:54:02 GMT

Mathcad 11 solves it without problems:

Then you can plot:

Success!
Luc

Re: Solving a system of 5 equations with 7 variables

-MFra- — Fri, 30 Dec 2016 10:59:17 GMT

Hi Werner,

fortunately I have based my answer on the header of the problem providing a generic example, but I have not even looked at the given system.

Bye

Re: Solving a system of 5 equations with 7 variables

ValeryOchkov — Fri, 30 Dec 2016 11:05:41 GMT

Volker Lehner написал(а):

Valery,

Can you explain me, how your Equation System will be solved symbolical by MathCad?

I tryed to reproduce it, but it fails...

I have Prime 3.1

Can you post your sheet?

Thank you

Volker

Sorry. You must have one vector with two equations not two vectors with left and right parts of equations.

Re: Solving a system of 5 equations with 7 variables

ValeryOchkov — Fri, 30 Dec 2016 11:08:50 GMT

Luc!

Send the Mathcad 11 sheet please!

Val

Re: Solving a system of 5 equations with 7 variables

Werner_E — Fri, 30 Dec 2016 11:14:28 GMT

F.M. wrote:

Hi Werner,

fortunately I have based my answer on the header of the problem providing a generic example, but I have not even looked at the given system.

Bye

Guess you mean UNfortunately.

Looking at the given system would not helped anyway as all you would have seen is a system with 5 equations and 7 variables.

Its Davids text around which made up for the real question and Lucs reply gave a hint how to solve the problem.

I wonder if there is a similar simple and compact solution without using the symbolics.

Re: Solving a system of 5 equations with 7 variables

-MFra- — Fri, 30 Dec 2016 11:31:07 GMT

No! no! just fortunately.... be banished bad luck ....

the user should strive to find the right solution ...

Re: Solving a system of 5 equations with 7 variables

Werner_E — Fri, 30 Dec 2016 12:10:07 GMT

F.M. wrote:

No! no! just fortunately.... be banished bad luck ....

the user should strive to find the right solution ...

???????????????????????????????????????????????????????????????

Do you really mean that you intentionally did not read the question?

Do you really mean that you intentionally gave an answer from which you knew that it would not be helpful?

Do you really mean that David should not have asked for help here because he should find the solution himself?

I can't believe it!!

Hope that I misunderstood your cryptic reply.

Re: Solving a system of 5 equations with 7 variables

-MFra- — Fri, 30 Dec 2016 13:21:22 GMT

... Basically, yes ... Today I have no time to lose and then to devote to the interpretation of themes written grossly ... I'm sorry for David. I'm not always available....

.....Are you the person to judge the work mine and of others? Your astonishment is offensive!

Re: Solving a system of 5 equations with 7 variables

LucMeekes — Fri, 30 Dec 2016 16:10:14 GMT

Here you go Valery.

Regards,

Luc

Re: Solving a system of 5 equations with 7 variables

LucMeekes — Fri, 30 Dec 2016 16:24:13 GMT

It is possible to separate the parts, but with '-' rather than '='.

Luc

Re: Solving a system of 5 equations with 7 variables

ValeryOchkov — Fri, 30 Dec 2016 17:09:55 GMT

Thanks, Luc.

It is for Этюд 6. Что почем или Старая задача на новый лад (Fig 6.16a)