On Nov 20, 2007 7:37 PM, Mike Hansen <[EMAIL PROTECTED]> wrote: > > Hmm... I just tested it on a newer version, and I get the incorrect > answer. I'll look into it more. >
It was similar to but not identical to 987 -- or more, it was that the fix for #987 wasn't sufficient. This is now fixd in #1215. William > > > On Nov 20, 2007 7:03 PM, Mike Hansen <[EMAIL PROTECTED]> wrote: > > This is ticket #987 which was fixed in 2.8.9. > > > > --Mike > > > > > > On Nov 20, 2007 5:37 AM, David Joyner <[EMAIL PROTECTED]> wrote: > > > > > > On Nov 20, 2007 8:12 AM, [EMAIL PROTECTED] > > > <[EMAIL PROTECTED]> wrote: > > > > > > > > As far as i know, length of curve, defined as > > > > f(x) > > > > from a to b (a <= x <= b) is > > > > L = integral from a to b of sqrt(1 + df(x)^2)dx > > > > where df(x) is diff(f,x) > > > > > > > > for f(x) = y = x^2 , a=0, b=2 it should be > > > > df(x)=2x > > > > sqrt(17) + ln|4 + sqrt(17)|/4 > > > > > > > > which is 4.647 > > > > > > > > however, SAGE thinks differently. For this code: > > > > > > > > y = x^2 > > > > dy = diff(y,x) > > > > z = integral(sqrt(1 + dy^2), x, 0, 2) > > > > print(z) > > > > print(RR(z)) > > > > > > > > output is > > > > > > > > 4 sqrt(17) + 4 > > > > -------------- > > > > 4 > > > > 5.12310562561766 > > > > > > > > Am i doing something wrong? > > > > > > No. Maxima gives > > > > > > (%i2) integrate (sqrt(1+4*x^2), x, 0, 2); > > > asinh(4) + 4 sqrt(17) > > > (%o2) --------------------- > > > 4 > > > > > > so possibly SAGE is not parsing that properly? That's the only thing I > > > can think > > > of. The following just confirms your computation: > > > > > > sage: sqrt(1 + (2*x)^2).nintegrate(x, 0, 2) > > > (4.6467837624329427, 1.5663635326179329e-09, 21, 0) > > > sage: integral(sqrt(1 + (2*x)^2), x, 0, 2) > > > (4 + 4*sqrt(17))/4 > > > sage: RR(integral(sqrt(1 + (2*x)^2), x, 0, 2)) > > > 5.12310562561766 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- William Stein Associate Professor of Mathematics University of Washington http://wstein.org --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://sage.math.washington.edu/sage/ and http://sage.scipy.org/sage/ -~----------~----~----~----~------~----~------~--~---
