Re: How to make the same two expressions

*To*: mathgroup at smc.vnet.net*Subject*: [mg119585] Re: How to make the same two expressions*From*: Peter Breitfeld <phbrf at t-online.de>*Date*: Sat, 11 Jun 2011 03:58:41 -0400 (EDT)*References*: <isss9i$jg1$1@smc.vnet.net>

Mariano Pierantozzi wrote: > Hi everyone, > i've this problem with Mathemtica: > i've got 2 expression depending on a and b: > expr1= -1.0019 - 1. Log[0.00190438 - 0.0249519 b] + (0.000040093 a > Log[0.152644/(0.152644 + 2 b)])/b > expr2=-1.00004 - 1. Log[0.0000378969 - 0.0249519 b] + (0.000040093 a > Log[0.0030376/(0.0030376 + 2 b)])/b > I want to make the same this two expressions. > The problem is that if i try to solve this is one equation in two parameter: > a and b. > So i think to put inside some value of a and b so i make equal the two > expression less than 10^-12 (for example) > I've to do a list of value: > b can vary beetwen -0.0015188 < b < 0.0015188 (the domain of logarithmic > function) and a must vary for example -2000 to 2000. > I can not find a waydo it. I try with list, and put the value inside, but > i've some problem. > if anyone can help I would be grateful... > Thank you! > > Mariano Pierantozzi > PhD student You may use FindInstance: lsg=FindInstande[expr1==expr2, {a,b}, Reals] Out= {{a -> 76.1255, b -> -0.00105906}} expr1-expr2/.lsg Out= {-8.88178*10^-16} -0.0015188 < b < 0.0015188 /. lsg Out= {True} -- _________________________________________________________________ Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de