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# Solve or Reduce: large system of equations

Posted 9 years ago
 Hi All, I am new to Mathematica and I would like to know why Mathematica isn't producing output for me. I put in my equations using Solve. It was saying 'Running...filename' for long. Then I thought may be it is because I am asking it to solve a large system of equations. So tried with the single equation used to demonstrate the function Solve on the website, yet it didn't solve. Can someone please help ease the burden of my initiation? Thanks. Yinka
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Posted 9 years ago
 It's beginning to work now Frank. Thanks.
Posted 9 years ago
 The complexity of Solve is probably almost as high as the complexity of Reduce. I assume your equations are nonlinear so what you're trying to do is probably NP hard. It would be useful if the documentation for functions gave their complexity.
Posted 9 years ago
 Thanks Frank, but both Solve and Reduce appear to be finding it difficult to converge to a solution.
Posted 9 years ago
 I believe MIchael Trott's book "The Mathematica Guide to Symbolics" says that Reduce is double exponential in complexity. That's why it is really only useful for problems with several variables.
Posted 9 years ago
 Bruce,Thanks for your response. Solve is working for the simple examples in the documentation now.Please advise on which is better Solve or Reduce if I have a system of 28 equations consisting of 41 unknowns (not including the parameters), but I want to solve these 28 equations for 28 endogenous variables in terms of the underlying structural parameters and the 13 exogenous variables? I would the results of each endogenous variables to be shown as analytical/algebraic expressions of the parameters and exogenous variables.Thank you.Yinka
Posted 9 years ago
 Do you get output for simple inputs (2+3)? Does Solve work for tiny examples (Solve[x+1==3,x]) ? Do the examples in documentation work for you? Do not put a semicolon after the Solve if you want output. If none of that helps, please attach a notebook file with inputs and outputs, or lack of outputs.