Re: root function

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Re^2: root function by psini (Deacon) on Jun 21, 2008 at 21:33 UTC
Yes it does. (-3)(1/3) results in nan; But so does the log approach, too. The odd roots of negative numbers must be treated separately as they are limit cases. I'd try something like: `if ($base>0) { return $base(1/$root); } elsif ($base==0) { return 0; ## or do manage the special case 00; } elsif ($root)==int($root) && $root%2==1) { return -((-$base)($root)); } else { return 'nan'; }` [download] Not tested, so probably broken :) Careful with that hash Eugene.	[reply] [d/l]
Re^3: root function by swampyankee (Parson) on Jun 21, 2008 at 21:40 UTC
The logarithms of negative numbers are defined; it's just that they require complex numbers to represent. It's not my fault that Perl (and C) can't cope with them ;-). All will become clear when one remembers that e^πi = -1 Information about American English usage here and here. Floating point issues? Please read this before posting. — emc	[reply]
Re^4: root function by psini (Deacon) on Jun 21, 2008 at 21:47 UTC
++ But I said that would not work, not that it is wrong. BTW, my math teacher preferred to write e^πi+1=0; she said that that form contains all the five really important numbers! Update: Well, she was a good teacher, now I realize she made that remark 31 years ago... and I still remember it Careful with that hash Eugene.	[reply]
Re^5: root function by swampyankee (Parson) on Jun 21, 2008 at 23:39 UTC
Re^4: root function by ysth (Canon) on Jun 22, 2008 at 06:53 UTC
Not complex numbers, series of complex numbers. e^(2n+1)πi = -1, for any integer n. Which makes them undefined, for at least some purposes. -- Online Fortune Cookie Search	[reply]
Re^5: root function by psini (Deacon) on Jun 22, 2008 at 07:14 UTC
Re^2: root function by ikegami (Patriarch) on Jun 21, 2008 at 21:37 UTC
linux: `$ perl -le'print -3 (1/3)' -1.44224957030741` [download] ActivePerl: `>perl -le"print -3 (1/3)" -1.44224957030741` [download] Update: Oops, precedence problem `$ perl -le'print( (-3) (1/3) )' nan` [download] `>perl -e"print( (-3) (1/3) )" -1.#IND` [download]	[reply] [d/l] [select]
Re^3: root function by psini (Deacon) on Jun 21, 2008 at 21:42 UTC
`sini@ordinalfabetix:~$ perl -le"print ((-3)(1/3));" nan sini@ordinalfabetix:~$` [download] Exponent operator has higher priority than unary minus so you are doing -(3(1/3)) instead of ((-3)(1/3)). This gives you accidentally the right result but it would tell you that square root of -2 == -1.414265... Careful with that hash Eugene.	[reply] [d/l]
Re^4: root function by ikegami (Patriarch) on Jun 21, 2008 at 21:58 UTC
Too slow! This gives you accidentally the right result but it would tell you that square root of -2 == -1.414265... But -1.414265... is a square root of 2. :) Update: Ack! ignore this post.	[reply]
Re^5: root function by sasdrtx (Friar) on Jun 21, 2008 at 23:17 UTC
Re^5: root function by psini (Deacon) on Jun 21, 2008 at 22:03 UTC