Re: math.nroot [was Re: A brief question.]

On Sun, 3 Jul 2005, George Sakkis wrote:

"Tom Anderson" <twic@xxxxxxxxxxxxxxx> wrote:

And finally, does Guido know something about arithmetic that i don't, or
is this expression:

-1.0 ** 0.5

Evaluated wrongly? 

No, it is evaluated according to the rules of precedence. It is
equivalent to -(1.0**0.5). You are confusing it with (-1.0)**0.5 which
fails as expected.


Ah. My mistake. I submit that this is also a bug in python's grammar.
There's probably some terribly good reason for it, though.

How about 'conformance with standard mathematic notation', does this count for a terribly good reason?

Yes. However, it's an excellent reason why python's precedence rules are wrong - in conventional mathematical notation, the unary minus, used to denote the sign of a literal number, does indeed have higher precedence than exponentiation: -1^2 evaluates to 1, not -1.

What would one expect to be the result of 5^2 - 2^2, 29 or 21? 

21.

Would you expect 5^2 + - 2^2 to be different, even if you write it as 5^2 + -2 ^ 2 ? 

Yes: 5^2 + -2^2 is 29, however you write it.

White space is not significant in math AFAIK ;-) 

No, but there's a very big difference between unary and binary minus.

tom

--
When you mentioned INSERT-MIND-INPUT ... did they look at you like this?
.

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