Solving a system of 5 equations with 7 variables

[dthunes]

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+mw

c=mf/mt

vf=mf/8.34

vw=mw/8.34

vt=vf+vw

Using the solve function only lets me solve for unknowns, so I'd have to rewrite the unknowns each time.

Using the find function requires me to guess, but I don't know how to distinguish from a known and a guess.

I could use if statements, but I'd have to write a huge set of formulas, which isn't ideal.

Any help would be appreciated.

[ValeryOchkov]

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.

[LucMeekes]

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

Luc

[vlehner]

This doesn't works in MathCad 3.1

MathCad maybe has a bug concerning like this...

[vlehner]

it doesn't work anyway in Prime 3.1

In MathCad 15 it works

very strange.

[ldante]

I think you miss something.

[vlehner]

This doesn't matter.

The dot is allways done.

Volker

[ValeryOchkov]

Better

[-MFra-]

Hi David,

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

Greetings FM

[Werner_E]

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.

[-MFra-]

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

[Werner_E]

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.

[-MFra-]

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

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

[Werner_E]

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.

[-MFra-]

... 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!

[Werner_E]

I am not judging in any way nor was any offensiveness intended. Looks you arequite sensitive concerning criticism.

My intention was to clarify because it looked to me that you misunderstood Davids question. It was only you next answer which made clear that you did not misunderstood the question but  you didn't even bother to read his question because of lack of time. And you wrote that you see it as a fortune that you didn't and David should find a solution himself. In my eyes THATS offensive. Its sure my problem, but thats hard to understand for me as its my understanding that the reason to reply to a question here is to help others.

I am just scratching my head and try to understand why someone would take the time to reply (even if it was just a large picture) to a question he had not read when he has "no time to loose"  and is "not available". Nobody expects anybody to be available, but I would not expect any reply from somebody who is not available, but maybe I am wrong in thinking so.

Anyway - Felice Anno Nuovo 2017!

[-MFra-]

Hi Werner,

By providing my example, it was my intention to suggest to David a way for the solution of non-homogeneous linear systems, with a number of unknowns greater than the number of  equations. And also that there is a broad theory about it, see the theorems of Roché and Capelli. Topics studied during the first year (or second semester) of the analysis course at the faculty of engineering.

Vielen Dank für Ihre guten Wünsche. Frohes Neues Jahr auch für Sie.

F. M.

P.S.

....Die besten Wünsche für ein frohes neues Jahr auch an Armin & co.