Re: circumference of an ellipse
- To: mathgroup at smc.vnet.net
- Subject: [mg19345] Re: circumference of an ellipse
- From: "Stephen P Luttrell" <luttrell at signal.dra.hmg.gb>
- Date: Fri, 20 Aug 1999 23:09:30 -0400
- Organization: Defence Evaluation and Research Agency
- References: <7p017c$778@smc.vnet.net> <7p301g$anl@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Allan Hayes <hay at haystack.demon.co.uk> wrote in message news:7p301g$anl at smc.vnet.net... > Marcel, > > circumference[a_, b_] := > Integrate[Sqrt[D[a Cos[t], t]^2 + D[b Sin[t], t]^2], {t, 0, 2Pi}] > >... (Preamble: I have $Version = "4.0 for Microsoft Windows (April 21, 1999)") I agree with this parametric solution, but it exposes a bug in Mathematica when you evaluate the following symbolic expression: circumference[a, b] This gives zero! Furthermore, if you define halfcircumference[a_, b_] := Integrate[Sqrt[D[a Cos[t], t]^2 + D[b Sin[t], t]^2], {t, 0, Pi}] and then evaluate halfcircumference[a, b], you get "Infinite expression 1/0 encountered". Steve Luttrell Signal Processing and Imagery Department DERA Malvern, St.Andrew's Road Malvern, United Kingdom, WR14 3PS +44 (0)1684 894046 (tel) +44 (0)1684 894384 (fax) luttrell at signal.dera.gov.uk (email)