Looking for derivative script

Question

I am desperately looking for a JavaScript that can calculate the first derivative of a function. The function always includes only one variable, x.

e.g. f(x) = x²
  f'(3) = 2x

Consequently, the script should deliver the result 6, since 2*3 = 6.

I hope you know what I mean.

Answer 1

function slope (f, x, dx) {
    dx = dx || .0000001;
    return (f(x+dx) - f(x)) / dx;
}

var f = function (x) { return Math.pow(x, 2); }

slope(f, 3)

Answer 2

Here's a Java library to help do such a thing:

http://jscl-meditor.sourceforge.net/

And another:

http://www.mathtools.net/Java/Mathematics/index.html

You can always use Rhino and import Java classes to use in your JavaScript.

Here's one for JavaScript:

http://code.google.com/p/smath/wiki/smathJavaScriptAPI