9 Nov
2007
9 Nov
'07
2:30 p.m.
On Nov 9, 2007 2:08 PM, Hans van Thiel
Hello All, Can anybody explain the results for 1.0, 2.0 and 3.0 times pi below? GHCi yields the same results. I did search the Haskell report and my text books, but to no avail. Thanks in advance, Hans van Thiel
Hugs> sin (0.0 * pi) 0.0 Hugs> sin (0.5 * pi) 1.0 Hugs> sin (1.0 * pi) 1.22460635382238e-16 Hugs> sin (1.5 * pi) -1.0 Hugs> sin (2.0 * pi) -2.44921270764475e-16 Hugs> sin (2.5 * pi) 1.0 Hugs> sin (3.0 * pi) 3.67381906146713e-16 Hugs>
More generally, this is due to the fact that floating-point numbers can only have finite precision, so a little bit of rounding error is inevitable when dealing with irrational numbers like pi. This problem is in no way specific to Haskell. -Brent