The other day I noticed a subtle bug in one of my Java visualization prototypes. I somehow got
NaNs everywhere, where there should absolutely be none of them.
The math I am using is correct, so I had to find the place where the
NaN was produced.
I would really like it if the whole application just blows up into my face when it tries to calculate something with
NaN instead of a usable value, but anyway, I had to trace the
NaNs to its origin and after some debugging I found it.
Math.acos (which I was using) has the following in its javadoc:
If the argument is NaN or its absolute value is greater than 1, then the result is NaN.
Duh. Better if I had read the javadoc before blindly throwing my values at the function, because, it turns out, I was passing a
1.000000000002 at some time, for which I got rewarded with
So, for a quick fix, I decided to ensure that my values are in the correct range of
Instead of writing something horrible like
if (val > 1.0) return 1.0; if (val < -1.0) return -1.0;
Leo gave me a much simpler and nicer looking solution:
return Math.max(Math.min(value), 1.0), -1.0);
These kind of floating-point errors are really nasty and I should probably take the time for reading "What Every Computer Scientist Should Know About Floating-Point Arithmetic" (Goldberg, 1991), finally.
I am writing these a-programmers-diary posts, for several reasons (at leats these are the ones to bring me starting this with this post).
The first one is, that I want to use this blog more for some kind of diary while programming. So do not assume that this will always be the best solution I am posting. Normally this is just the one I found working and seemed to me not as a crime against humanity.
Another reason is, that I sometimes think 'Oh, I had this problem before, how do I solve this'. So I can use these posts for some kind of reference.
The third reasons is that maybe someone reads this and finds a better solution or spots any mistakes I am making. If you do so feel free to correct me, I really like to learn. Just contact me via mail or twitter and I will add your suggestions as an update to the post, so it stays with the text of the post and does not get lost like outsourced comments like to do.