On Wed, Jun 24, 2009 at 08:46:04PM -0300, Aaron MacDonald wrote:
Is there anything in Haskell that can represent doubles with higher ^^^^^^^
No, I'm pretty sure "double precision" will be double precision everywhere (systems not supporting IEEE-754 notwithstanding.) Want to represent floating point numbers more precisely? That's feasible.
precision than the regular kind? I'm working with formulas that generate sets of values, and values that I know should be zero are ending up as things like -7.105427357601002e-15 or -1.7763568394002505e-14, which is causing all kinds of butterfly effects.
I've heard of Rational, but I need to also work with irrational numbers (namely, pi and anything that comes from cos and sin). What other options do I have?
Some systems have support for "long doubles", typically an 80-bit type on x86; I don't know if Haskell provides any access to this. I doubt it. If you want a more sledgehammerish approach, packages like HMPFR: http://hackage.haskell.org/package/hmpfr can provide arbitrary precision calculations. They're slow, though. More to the point, however: you don't want more precision. Welcome to the world of numerical algorithms; floating point arithmetic is inherently inexact. Get used to it. For example, I'll bet your errors are caused by testing for equality against zero, and if I had to guess, you're probably trying to terminate a procedure when some value hits zero? It's not going to; you need to introduce the concept of tolerances, and accept if |val| < tol. This is a simplistic solution and not really right in most cases, but might help. If you want more advice about how to handle floating-point inaccuracy, could you provide a program and what's going wrong? For way more information, consult "What Every Computer Scientist Should Know About Floating-Point Arithmetic." http://docs.sun.com/source/806-3568/ncg_goldberg.html HTH, AHH