How to solve a equation system with more constraints than unkwons?

[bishmastornelli]

I'm using mathcad to solve an equation system with Given and find.

I had 10 variables (or unkwon values) and 10 equations. My call to find was with 10 parameters.

The problem I'm facing now is that I found the real value for 1 of those 10 variables and now I don't know what equations to remove.

With that known value, I can use one of the equations to find another value and thus, I have 2 known values. I remove that equation but nowI have to remove one more because I have 9 equations for 8 unkowns.

The problem is that when I remove equations 4, 5, 6, 7, 8, 9 or 10 then I get an error about unkown variables not defined or I get not real values but when I remove equation 2 or 3, I get real values but very different.

How can I choose the equation to remove or use more equations than unkown values?

 

[IRstuff]

Why are you removing any equations? All this means is that you have 10 equations and 9 unknowns, which is not a serious problem. However, you may want to use Minerr() rather than Find, in case the solution that you think you already have is overly constraining.

TTFN
faq731-376

 

[bishmastornelli]

I wanted to remove equations because Find needs 1 constraint for each unknown or that's what I think.

I just tried to use Minerr with 10 constraints and 9 unknowns the values I get for 6 of those unkowns are extremely dependent on the initial value and the answer is not close to what I think it should be.

When using Find with 10 constraints and 9 unknowns I get an error.

 

[IRstuff]

I suggest that you review your equations to make sure that there is actually a solution.

TTFN
faq731-376