# [racket] Multiplying by 0

On Feb 14, 2011, at 3:26 PM, David Van Horn wrote:
>* On 2/14/11 3:14 PM, Sam Tobin-Hochstadt wrote:
*>>* No, it's not a bug. Since 1e100 is an inexact number, there's
*>>* uncertainty about the minimum of those two numbers, and the result is
*>>* therefore inexact.
*>*
*>* I would've expected min to return a number that is `eq?' to one of its arguments.
*>*
*>* In other words, what is wrong with this definition of `min'?
*>*
*>* (define (min n1 n2)
*>* (cond [(<= n1 n2) n1]
*>* [else n2]))
*
What's wrong with this is that, mathematically, since 1e100 is inexact, we're not CERTAIN it's >= 0, so the "proper" answer to (<= n1 n2) is not true but rather almost-certainly-true. (An "inexact Boolean", if you will....)
When you define the function as above, the "<=" takes its best guess as to which number is really smaller and pretends that the answer is certain.
Stephen Bloch
sbloch at adelphi.edu