Config Object rather than positional API

[CrossEye]

I like this idea quite a bit. But your API is a little... well, crowded might be a good word. I think that, rather than a positional parameter list, a configuration object would provide both more flexibility and better readability:

    goalSeek({
        testFunction: function(a, b, c) {return a * b * c;},
        goal: 140,
        params: [4, 5, 3],
        position: 2,
        tolerance: 0.01,     // optional
        maxIterations: 1000  // optional
    });
    //=> 7

    goalSeek({
        testFunction: function(i, o) {return i * o.a  o.b.b1;},
        goal: 140,
        params: [4, {a: 5, b: {b1: 3}}],
        position: 2,
        prop: "b.b1",        // optional
        tolerance: 0.01,     // optional
        maxIterations: 1000  // optional
    });
    //=> 7

The other thing I would suggest is that allow an undefined value as the starting choice for the target parameter. I know that this would make the algorithm harder to get off the ground; you'll have to go seeking for an appropriate initial value that works. But it could lead to a nicer user experience, using a token such as __ (which is not defined) as a placeholder:

    var __; // (undefined)
    //...
    goalSeek({
        testFunction: function(a, b, c) {return a * b * c;},
        goal: 140,
        params: [4, 5, __], 
        position: 2,
        tolerance: 0.01,     // optional
        maxIterations: 1000  // optional
    });
    //=> 7

Note the change to params. This makes it much clearer what you're looking for.

(I also posted this suggestion on comp.lang.javascript, where I first saw this.)

[adam-hanna]

Thanks for the suggestions! I'll definitely make the changes.

I'll also be extending the root method beyond the Steffenson model to include secant and a modified secant method.

[CrossEye]

I'll be interested to see the extensions to other methods.

One thing I didn't say was that, at least for the simple parameter-position-only case (I'm not so sure about the object-property one), the __ as placeholder also should allow the user to skip the position parameter.

Very interesting work, in any case.

[adam-hanna]

Incorporated your ideas. Thanks for the input!

I'll add the secant root method asap (sometimes the steffenson method doesn't converge).