On Sun, 23 Nov 2008 19:39:54 +0530, Arun Tomar wrote: > hi! > > > On Sun, Nov 23, 2008 at 5:07 PM, David <[EMAIL PROTECTED]> wrote: >> Hello everybody, >> >> I recently came across a book by Prof. Langtangen: Indroduction to >> Computer Programming: >> http://folk.uio.no/hpl/INF1100/INF1100-ebook-Aug08.pdf >> >> I am trying to solve exercise 1.18 ("Why does the following program not >> work correctly?"), but I don't find the mistake: why does the line >> >> q = sqrt(b*b - 4*a*c) > > problem here is that the method sqrt doesn't accepts -negative numbers > which in this case is the outcome of the expression above. to rectify > that u can use the following > > q = sqrt(math.fabs(b*b - 4*a*c)) > > basically convert the negative number to absolute number, rest of the > stuff will work. >
An alternative solution would be to use the sqrt from cmath module, which does handle negative root by outputting complex number: a = 2; b = 1; c = 2 from cmath import sqrt q = sqrt(b*b - 4*a*c) x1 = (-b + q)/2*a x2 = (-b - q)/2*a print x1, x2 output: (-1+3.87298334621j) (-1-3.87298334621j) This would be the most mathematically correct solution without changing what the program _seems_ to meant. However, what the program _actually_ meant, I don't know. Python's math module does not handle complex numbers because many day-to- day scripters doesn't have strong mathematical background to handle complex number, or they simply doesn't need to use complex number, or sometimes complex number solution is -- for their particular problem -- an indication that something is not right. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
