Talk:Special factorials: Difference between revisions
→Reverse factorial algorithm: Fixed syntax highlighting
(Demonstrate an efficient, readable reverse factorial algorithm) |
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=== Reverse factorial algorithm ===
I took a stab at translating the reverse factorial algorithm used in the Factor entry to Java. It should be almost as efficient as taking the factorial itself.
<syntaxhighlight lang="java">
if (n == 1)
return 0; //1 has two answers -- return the lower one
int a = 1;
int b = 1;
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return b;
else return -1; //undefined
}
</syntaxhighlight>
--[[User:Chunes|Chunes]] ([[User talk:Chunes|talk]]) 17:06, 16 March 2021 (UTC)
: Note that the ''factorial inverse'' (or ''reverse factorial'') of '''unity''' has two possible answers: '''zero''' and '''unity'''.
: It is normal when searching a series (in this case, the series of factorial products) to use the first match found in the series. -- [[User:Gerard Schildberger|Gerard Schildberger]] ([[User talk:Gerard Schildberger|talk]]) 17:37, 16 March 2021 (UTC)
:: Good catch. I revised the algorithm above and will make a note about it in the task description. --[[User:Chunes|Chunes]] ([[User talk:Chunes|talk]]) 17:58, 16 March 2021 (UTC)
=== Why is af(0) 0? ===
Is it that 0 is the additive identity the way that factorial of 0 is 1 is the multiplicative identity? If so why should it be the identity anyway?
: I think it's just that the formula literally produces 0 for n = 0.
: First run through, i is 1, this produces -1. Second run through, i is 0, this produces 1 and their sum is 0. --[[User:Chunes|Chunes]] ([[User talk:Chunes|talk]]) 17:36, 16 March 2021 (UTC)
So the math summation notation goes backwards automatically when i > n? This may make a good task -- C will do one iteration and stop, etc. --[[User:Wherrera|Wherrera]] ([[User talk:Wherrera|talk]]) 21:11, 16 March 2021 (UTC)
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