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

[Terry Hancock]

On Sunday 03 July 2005 10:47 pm, Steven D'Aprano wrote:
> Any floating point package that supports the IEEE 
> standard should give you a test to see if a float 
> represents a NaN. That's what you need. You certainly 
> can't rely on "x == SOME_NAN" because there are 254 
> different NaNs.
> 
> There is no sensible reason to test equality of NaNs. 
> It is logically nonsense to say that one NaN is equal 
> to another, as such a thing implies contradictions like 
> -1==-2. If you support IEEE, you will have a test for 
> NaNs, so you can detect them when you need to.

I have to mention that the idea of a math package that 
allows NaN to propagate as though it were a number 
scares the willies out of me.  God help me if I were to use
it on something like Engineering where lives might
depend on the answer being right.

That'd be like having a math package that allowed,
say 0/0 = 1 or Inf/Inf = 1.  It's not hard at all to come
up with dozens of problems for which that is the WRONG
guess -- getting an actual answer for dividing two
infinities requires using limits and calculus.  The reason
Inf/Inf isn't defined is that it can actually be just about
any number --- finite or infinite.

I can seriously imagine structures breaking and collapsing
because they were designed using such a package, and
a NaN was generated and missed somewhere.

Really, the only *right* thing to do is to raise an exception
ASAP after the NaN comes up.

On a more practical note, *is* there a isNaN() function? Seems
like it ought to be in the math module.   Looks like you have
to do it through "fpectl" as things stand.

Is anyone else bothered that "math" and "cmath" are in the
"Miscellaneous Services" section of the LR? Seems like we
ought to get Numeric and/or Numarray and group all of
these in a separate "Math & Science" section.

--
Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com