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> [problem with doing]  pow(2, -12)
When passing integer arguments to pow(), or any other
math function requiring floating points (double, actually),
be sure that you either cast the variable, e.g.

	pow((double) i, (double) j)    ,

or explicitely type the decimal point, e.g.

	pow(2., -12.)    .

While most compilers handle implicit type conversion in
*expressions*, arguments to *functions* require more care.

The particular problem you are having bit me once before,
although I didn't get a useful runtime error message, just
the old "(core dumped)."  I don't think the negative exponent
is the problem.  A negative mantissa, however, will not work,
even if the exponent is integer.

			Hope this helps,

			Ron Ueberschaer		
			SRI International 	Menlo Park, CA
			...!{hplabs,rutgers}!sri-unix!ubi
			ubi@sri-unix.UUCP

In article <226@cogent.UUCP>, mark@cogent.UUCP (Captain Neptune) writes:
> 
> I am running an HP 9000/840 running HP-UX and I have a problem doing some math.
> I am trying to use pow(3M) to raise a positive integer value to a negative
> integer value.  For example, the 12th root of 2 --> 2 ^ (-12) --> pow(2,-12).
> 
> I keep getting "DOMAIN error" even though the manual page doesn't seem to
> cite this case as an illegal one.  It would be illegal if, say, the first
> argument was zero, for instance.  Pow(3M) is found on the manual page for
> "exp(3M)".

My guess is that you have neglected ensure that the arguments passed to pow
are doubles. try pow(2.0, -12.0);
BTW the 12th root of 2 is 2^(1/12) i.e. pow(2.0, 1.0/12.0);

V7 and BSD man page say that pow gives domain error when 2nd argument
is negative and non-integral. This is wrong. SYSV man page correctly
states that domain error results when 1st arg is negative and 2nd is
non-integral.

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+ In article <226@cogent.UUCP> mark@cogent.UUCP (Captain Neptune) writes:
+    [...]
+ integer value.  For example, the 12th root of 2 --> 2 ^ (-12) --> pow(2,-12).
+    [...]
+   Have I made some fundamental blunder?

Yes.  2^(-12) is *NOT* the 12th root of 2.  It is the 12th power of 1/2.
[As for the matter at hand, your pow(3M) problem, I have no answer.  Sorry,
but I couldn't let this one go by.]

> I am trying to use pow(3M) to raise a positive integer value to a negative
> integer value.  For example, the 12th root of 2 --> 2 ^ (-12) --> pow(2,-12).
> 
> Any ideas why this is happening?  Have I made some fundamental blunder?
> Has pow(3M) made some fundamental blunder?

    You have made two fundamental blunders.  First, the arguments to pow() are
doubles, so the correct way to all the function is:

	pow(2.0, -12.0);

   The second blunder is that 2 ^ -12 == 1 / (2 ^ 12), NOT 12th-root 2!  The
code for that would be:

	pow(2.0, 1.0 / 12.0);

    I suggest using 2^-12 would generate a useless musical scale (the only
practical application of 12-th root 2 I know about).

					John Worley
					hplabs!dana!worley