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-   -   Re: Algorithm to solve equation for variable (http://www.velocityreviews.com/forums/t123793-re-algorithm-to-solve-equation-for-variable.html)

 pete kirkham 06-27-2003 10:39 PM

Re: Algorithm to solve equation for variable

Dan wrote:

> I am looking for an algorithm to solve an equation for any particular
> variable. For example, if I have the equation y = w * h + l (actually
> I have y = w h * l + because I'm using postfix notation), I need an
> algorithm that can solve the equation for any of w, h, l.
>
> I only support the four basic operators in my equations ( + - * / )
> and do not support functions. The way I store the equation is in a
> container; each item in the container is either a variable name or an
> Integer representing the operation, where + is 2, - is 3, * is 4 and /
> is 5.
>
> Any assistance would be much appreciated.
> Dan

If you are solving for one variable with the other variables fixed, then
use some form of evaluator (as a compiled function, an abstract tree or
iterpreted directly) for the function and an itertive solver (Mueller,
Newton Raphson, etc). As David said, for less than 5th order analytical
solutions exist.

If you are solving for multiple variables, then you either need more
equations and use a matrix method, or use some form of heuristic space
search.

It is possible to solve multi-variate problems iteratively by
compositing loops; it's why we still have crays in the basement at work.

Pete

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