Re: [R] precision problem

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Thu 26 May 2005 - 01:34:41 EST

Omar Lakkis wrote:

>I have prices that I am finding difficult to compare with ==, > and >,
>due to precision. For example: the numbers should match, with '==',
>but they differ in the magnitude of 1e-14 due to bunch of calculations
>that I run on them. Programming with java, I am used to implementing a
>function that compares the difference between the numbers to a pre
>determined precision factor. This could be very slow when I have two
>matrices of numbers that I could otherwise compare with a simple '==',
>'>' or '<' in R.
>What is teh best solution for this problem?
>Can I control the precision of ==, > and < without having to
>reimplement the operations in a slow way?
>

The somewhat misleadingly named "all.equal()" function does what you want for ==. For the inequalities, you may want to add some constant to one side, e.g.

x > y-.Machine$double.eps ^ 0.5

instead of x > y.

Duncan Murdoch



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