pip calculator

denp, I finally got round to having a good look at this PipCalculator of yours - I understand most of what you have done, but the asInverse function has me a little lost. This is what I'm doing to test it - it isn't very sophisticated, but it works for me.

The code:

                    PipCalculator pip = new PipCalculator();
                    double cp = rp.getBestPricesToBack().getPrice().get(0).getPrice();
                    System.out.println("Current price = " + rp.getBestPricesToBack().getPrice().get(0).getPrice());
                    System.out.println("pip addPips + 1 = " + pip.addPips(cp, 1));
                    System.out.println("pip addPips + 2 = " + pip.addPips(cp, 2));
                    System.out.println("pip addPips + 5 = " + pip.addPips(cp, 5));
                    System.out.println("pip addPips + -1 = " + pip.addPips(cp, -1));
                    System.out.println("pip addPips + -2 = " + pip.addPips(cp, -2));
                    System.out.println("pip addPips + -5 = " + pip.addPips(cp, -5));
                    System.out.println("pip asInverse = " + pip.round(pip.asInverse(cp)));

The results:

Current price = 2.22
pip addPips + 1 = 2.24
pip addPips + 2 = 2.26
pip addPips + 5 = 2.32
pip addPips + -1 = 2.2
pip addPips + -2 = 2.18
pip addPips + -5 = 2.12
pip asInverse = 0.45

As you can see, the results for adPips are pretty much what I am expecting (and just as a by the by, exactly what I needed, thanks very much!) but I'm not completely understanding what the asInverse function is returning.

This is the function as you have written it:

    public double asInverse(double p) {
        return p > 0 ? 1 / p : 0.0;
    }

Which I have to confess I didn't understand at all. So after another look at the java operators, this is the function as I would have written it - yours is much more elegant than mine:

    public double asInverse(double p) {
        double result = 0.0;
        if (p > 0)
        {
            result = 1 / p;
        }
        return result;
    }

So I understand the operation of the method, but what is the point of the result?

Just as a by the way, even if you never answer this, I'll be grateful for that code, I can't count how many times I have wished for a shorter way for if, then, else statements. Next time I'm working on picking up a new language, I won't brush past the operators like I did with Java.

Cheers,

Alan

I've done a little more experimenting with it and I'm even more confused than before. Probably is me being thick. I had a look at inverse functions and what they are used for (wikipedia) and I think I have a handle on them. I'm still not seeing how to use this function in this class.

This is what I've done:
    PipCalculator pip = new PipCalculator();
    double cp = rp.getBestPricesToBack().getPrice().get(0).getPrice();
    System.out.println("Current price = " + rp.getBestPricesToBack().getPrice().get(0).getPrice());
    System.out.println("pip addPips + 1 = " + pip.addPips(cp, 1));
    System.out.println("pip addPips + 2 = " + pip.addPips(cp, 2));
    System.out.println("pip addPips + 5 = " + pip.addPips(cp, 5));
    System.out.println("pip addPips + -1 = " + pip.addPips(cp, -1));
    System.out.println("pip addPips + -2 = " + pip.addPips(cp, -2));
    System.out.println("pip addPips + -5 = " + pip.addPips(cp, -5));
    System.out.println("pip asInverse = " + pip.round(pip.asInverse(cp)));
    System.out.println("pip asInverse + 1 = " + pip.round(pip.asInverse(pip.addPips(cp, 1))));
    System.out.println("pip asInverse + 2 = " + pip.round(pip.asInverse(pip.addPips(cp, 2))));
    System.out.println("pip asInverse + 5 = " + pip.round(pip.asInverse(pip.addPips(cp, 5))));
    System.out.println("pip asInverse + -1 = " + pip.round(pip.asInverse(pip.addPips(cp, -1))));
    System.out.println("pip asInverse + -2 = " + pip.round(pip.asInverse(pip.addPips(cp, -2))));
    System.out.println("pip asInverse + -5 = " + pip.round(pip.asInverse(pip.addPips(cp, -5))));

this is the result I get:

    Current price = 1.48
    pip addPips + 1 = 1.49
    pip addPips + 2 = 1.5
    pip addPips + 5 = 1.53
    pip addPips + -1 = 1.47
    pip addPips + -2 = 1.46
    pip addPips + -5 = 1.43
    pip asInverse = 0.68
    pip asInverse + 1 = 0.67
    pip asInverse + 2 = 0.67
    pip asInverse + 5 = 0.65
    pip asInverse + -1 = 0.68
    pip asInverse + -2 = 0.68
    pip asInverse + -5 = 0.7

Just for this example, I can see that the difference between the current price and the asInverse return is 0.2 Just looking at the returns from a couple of  different price calls now:

    Current price = 1.04
    pip asInverse = 0.96

    Current price = 1.12
    pip asInverse = 0.89

I don't understand. I think it may be giving the number of ticks left until the next jump, but that makes no sense at all if you look at the very first lot of output there. I'm horribly confused here and I think I might be overthinking the problem.

Alan

lol, you'll kick yourself!

A runner at a price of 1.04 will win 0.96 (96%) of the time.
A runner at 2 (ie evens) will win 0.5 (50%) of the time

All the inverse function does is convert either way between implied probability and betfair prices

1 / 2 = 0.5 and back again 1 / 0.5 = 2

Oh for christs sake.

Consider my arse thoroughly self kicked.

Thats actually a really useful function though - I have a real use for that at the moment.

Thanks Fred,

Alan

Sorry Alan - I should have thought about it more and used a name such as Fred suggests.

p > 0 ? 1 / p : 0.0;

is an example of the "ternary operator".  All it is doing in this case is avoiding a divide by zero error.  The ternary operator is available in many languages.  Oddly it only got added to Python in version 2.5 a year or so ago.

no biggy denp, if nothing else it showed me how capable I am of overthinking something. I think I sometimes need to back off and reduce things to basics. As you saw, I have a shocking tendency to make things more complicated than they are.

As for the ternary operator, I love it, I think I will be using that structure a lot. Lesson learned though, I'm going to document it when I do though - I find reading my own code an adventure in unintelligibility most of the time, reading someone elses code often throws me for a spin.

On the subject of python though, I just bought myself a Nokia e61i off ebay and I was gratified to find that not only is python supported on it, there is an interactive shell for it as well. All I need now is a decent free text editor for it and I'll start playing with it on the boring days at work when I can't get my laptop out.

Thanks again,

Alan

Very useful class. It saves my time. Thank you.

I made some modifications of code for using with the Swing JSpinner component.

All that you need - add code below to your component initialization.

JSpinner mySpinner = new javax.swing.JSpinner();
mySpinner.setModel(new PipModel(1.01));
mySpinner.setEditor(new PipEditor(mySpinner));

Attachment: PipEditor.java (0.0KB)

Attachment: PipModel.java (3.0KB)