Re: Getting crude approximation to a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg58845] Re: Getting crude approximation to a function*From*: dh <dh at metrohm.ch>*Date*: Thu, 21 Jul 2005 03:07:53 -0400 (EDT)*References*: <dbkkpu$s6a$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Mukhtar, with version: 5.1 for Microsoft Windows (October 25, 2004) your input produces a fully rationalized output: -13/3 + (2*x)/3 + (71*p*x)/100 sincerely, Daniel Mukhtar Bekkali wrote: > Assume I have a function f[x], x is some variable, given below (my real > function is much more complex). I would like to obtain its crude > approximation. I used command Series, first order expansion. The > resulting function has coefficients that have high precision. I do not > need that since my expansion is very crude anyway. I need coefficients > that are rational number approximations to these coefficients. How do I > obtain this? It seems to me that command Chop takes care of > coefficients that are not product with variable x but cannot handle > coefficients that are not standalone. For instance, in this example > > \!\(\(\(Normal[ > Series[0.71 p\ > x + \(1\/3\) > x\^2 - 4, {x, 1, 1}]] // Expand\) // Chop\) // > Rationalize\) > > I would like to obtain output of the form (-13/10)+(29/10)x. > Mathematica gives me (-13/10)+2.8972x instead, where it keeps > 2.8971974507154195` in the memory. I need this because I use > InequalitySolve package and it refuses to function unless all numbers > are rational. > > Mukhtar Bekkali >