@Carl Love 

Yes, you're so right. I'm sorry that I dind't give this information. It's a Markov chain. The matrix M is a 7x7 stochatics matrix (all entries nonnegative; each row sums to 1). 

But the entries in the matrix aren't specific values, the entries are formulas depending on the variables a,b,c,d,e,f,g. (I also dind't give this information.)

So the problem is to solve this without values, getting formulas for each of the variables a,b,c,d,e,f,g depending on z if thats possible. 

Here one example of one of the 7 equations: 

b/(4*a + 2*b + 2*c) + f*(1 - 1/(b + c + 2*d + 2*e + f + g)) = f

If you have any other idea I would be very glad to hear about it. 

Hey @Kitonum thank you very much for responding to my question.

Thanks for the tip, I was looking this up, but not really sure how to put my problem in the form of the LeastSquare. 

Following the formulation of my problem: I want to fin the solution for each a,...,g, in the end I would like to have formulas for each depending from z. Or I could put a concrete value for z and find a numeric solution for each variale.

May you could give me another advice how to bring this with the LeastSquare command in connection. Thank you so much!