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## Variable undefined, 7 equations

Hi!

I am trying to solve 7 equations with 7 variables.

I have tried several things but I just can't get it to work. Mathcad keeps saying variable undefined and I have no clue about what's going wrong..

Can anyone help me out please? I need it for my thesis.

Greets,

Martijn

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2 REPLIES 2

## Re: Variable undefined, 7 equations

Several of your 0.5s were written as 0,5.

Alan

## Re: Variable undefined, 7 equations

Apart from the typos, which Alan pointed out, it is noticeable, that your system has an infinite number of solutions. The rank of the 7x7 coefficient matrix it only 2. Depending on the rank of the extended matrix in your case you can chose 5 variables as you like and calculate the remaining 2.

If you solve numerically, Mathcad choses the "inner" five variables to be zero and calculates A and G. If you evaluate symbolically, the symbol processor choses the last five variables to be zero and calculates A and B.

If you use "fully" with the symbolic eval, Mathcad shows you how to calculate A and B if you chose the remaining five to be any values you wish.

I have no idea where these equations stem from, but I could image, that it should be a(B,C,D,E,F,G)=A (instead of =0) and so on with the rest. You will get a nice unique solution that way - just a guess.

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