Feature #1490
New function: MinusOneToPower
Description
I have just seen in the code for matrix adjoint power(-1, i+j).
It would be nice to have a simpler function for computing a power of -1.
If so, what should it be called?
History
#1
Updated by John Abbott over 3 years ago
Updated by There is a very simple inline impl:
long MinusOneToPower(long n)
{
return (IsEven(n)?1:-1;
}
If we do accept this fn, in which (header) file should it go?
#2
Updated by Anna Maria Bigatti over 3 years ago
Updated by John Abbott wrote:
There is a very simple inline impl:
[...]If we do accept this fn, in which (header) file should it go?
Just after power(long, long), I'd say
#3
Updated by John Abbott over 3 years ago
- Status changed from New to In Progress
- % Done changed from 0 to 10
It would be tricky to call the function power because I want the return type to be long (or even int) rather than BigInt.
The power function (family) in BigIntOps all return BigInt which is a bit wasteful -- more irritating than exorbitantly slow.
Possible names include MinusOnePower or MinusOneToPower; here the "minus one" is in the name rather than as an explicit argument.
JAA thinks there ought to be a better (compact) name... but what?
UPDATE nor more compact, but possibly better PowerOfMinusOne, at least it starts with Power which is like power.
#4
Updated by John Abbott over 3 years ago
- Status changed from In Progress to Resolved
- Assignee set to John Abbott
- % Done changed from 10 to 70
I have implemented PowerOfMinusOne (for both MachineInt and BigInt exponents).
Currently they are not inline; should I make them inline? (seems to be harmless)
No doc; no tests.
#5
Updated by John Abbott over 3 years ago
Now I am having doubts about this function...
The normal power function just calls mpz_power, and I fully expect that this GMP function handles "cleverly" the case of high powers of 1, 0, and -1.
The only advantage MinusOneToPower has is that the result is a long rather than a BigInt; but when is that a genuine advantage?
So now, I'm considering deleting the impl, and rejecting this issue.
What do you think?
#6
Updated by John Abbott over 3 years ago
- Status changed from Resolved to Rejected
- % Done changed from 70 to 100
- Estimated time set to 0.99 h
REJECTED
There is no need for MinusOneToPower; it can be achieved by SmallPower (if we want to avoid BigInt) or by power (with the overhead of creating a BigInt).
I have removed the fn defn, and the doc.