Re: A simple error
- To: mathgroup at smc.vnet.net
- Subject: [mg102158] Re: A simple error
- From: Alois Steindl <alois.steindl at jet2web.cc>
- Date: Fri, 31 Jul 2009 05:53:47 -0400 (EDT)
- References: <h4rpen$l85$1@smc.vnet.net>
Youness Eaidgah schrieb: > Dear all, > I have faced a awkward situation in Mathematica. I want to sum the following > simple equations: > > DTEP12 = 0.11 (80000 - 12000 P + 800000 (1 - R)) + 0.11 (40000 - 12000 P + > 1000000 (1 - R)) + 0.28 (-12000 P + 1200000 (1 - R)) > MTEP12 = 0.11 (-130000 + 12000 (-35 + P) + 800000 R) + 0.11 (-130000 + 12000 > (-35 + P) + 1000000 R) + 0.28 (-130000 + 12000 (-35 + P) + 1200000 R) > > Obviously, the result of the DTEP12+MTEP12 is : 272200 > > However, when I use the following commands > > Simplify[DTEP12+ MTEP12] or FullSimplify[DTEP12+MTEP12] > > Mathematica returns: 272200.+ 0. P + 5.82077*10^-11 R. I am suprised where > the last term comes form (5.82077*10^-11 R)! It is a really really small > value, however, it is still an error. it creates some inconveniences later > in my calculations. I would appreciate if you could help me out. > Thank you, > Youness > > Hello, question like yours are asked here almost daily: As soon as you use floating point numbers, rounding errors happen. In your example you could replace 0.11 by 11/100+eps1 and 0.28 by 28/100+eps2. You should definitively learn about the calculation with floating point numbers (just reading more recent questions and answers in ths groupd could help considerably.) Alois