At 04:31 PM 2/13/02 +0200, you wrote:
>hello everybody , i want to learn how can i solve quadratic equations
>by using 16f84. i have 4 equations with 4 unknowns .

Which is it? A "quadratic" equation is one in the form a*x^2 + b*x + c = 0,
there are two solutions which may be real or complex. You can get the
solution from any book

x = (- b +/- sqrt( b^2 - 4*a*c))/(2*a)

But it sounds like you just have 4 linear equations in 4 unknowns,
in which case you can simply use Gaussian elimination or some other
textbook method of solving a system of linear equations.

Implementing it can be done in C or in assembly with math routines,
there's nothing here that isn't straightforward except for the details
which will get you every time. ;-) In particular poorly conditioned
linear systems can require much more precision in the calculations
than what you need in the result. See any textbook on Numerical
Analysis for the details, which take a chapter or two. You can imagine
the matrix defining your linear system to describe a 4-dimensional
elliptical form, the closer to a sphere it looks, (matrix condition
number of 1) the better your results will be for a give precision of
calculations and coefficients, the more elliptical it looks, the
more trouble you are in. The condition number is just the ratio of
the largest to smallest eigenvalues.


Some useful algorithms are available in the book "Numerical Recipes in C",
which you can find on the web.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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