Precision Problems
- To: mathgroup at smc.vnet.net
- Subject: [mg19210] Precision Problems
- From: "Holger Strauss" <strauss at ika.ruhr-uni-bochum.de>
- Date: Tue, 10 Aug 1999 02:53:00 -0400
- Organization: Ruhr-Universitaet Bochum, Rechenzentrum
- Sender: owner-wri-mathgroup at wolfram.com
Hi, I have some numerical precision problems (Mathematica 3.0) with the following code: <<Graphics`Graphics` f3[x_] := 20 Log[10, 1/(15120 x^4)*(-90720 - 15120 x^2 + 13424 x^4 + 9 (13440 + 2240 x^2 + 257 x^4) Cos[x] - 72 (420 + 70 x^2 + 9 x^4) Cos[2x] + 31 x^4 Cos[3x])] LogLinearPlot[f3[x], {x,0.05,Pi}] As can be seen from the plot, evaluating f3 doesn't work for small arguments. It seems to me that this is the result of large numbers being subtracted from each other resulting in a very small difference. It it possible to increase the precision of the calculation adequatly? I already tried to encapsulate the whole function with N[..., 50000], however, without success... Is there any other way of successfully evaluating and plotting f3 for small arguments? Holger