[Numpy-discussion] arange and floating point arguments

Christopher Barker Chris.Barker@noaa....
Sat Sep 15 00:12:34 CDT 2007


Robert Kern wrote:
> Here's the thing: binary floating point is intrinsically surprising to people
> who are only accustomed to decimal.

Very good point. Binary arithmetic is NOT less accurate that decimal 
arithmetic, it just has different values that it can't represent 
exactly. So one is surprised that 1.0/3.0 isn't represented exactly!

The confusion stems from th fact that we use decimal literals, even when 
using binary arithmetic, but you just need to learn to get used to it.

For what it's worth, the MATLAB mailing list has a constant trickle of 
notes from new users along the lines of "MATLAB is broken!" when they 
have encountered binary-decimal issues like these. It is inescapable.

Binary representation was one of the first things I learned in my first 
computer class , using Basic, over 25 years ago (am I really that old!). 
You really need to learn at least a tiny bit about binary if you're 
going to do math with computers.

Oh, and could someone post an actual example of a use for which FP 
arange is required (with fudges to try to accommodate decimal to binary 
conversion errors), and linspace won't do?

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer

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