Re: Abs in the denominator

*To*: mathgroup at smc.vnet.net*Subject*: [mg128566] Re: Abs in the denominator*From*: David Bailey <dave at removedbailey.co.uk>*Date*: Sun, 4 Nov 2012 20:11:32 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <k6vj61$6b4$1@smc.vnet.net>

On 02/11/2012 04:45, Dieter Ernst wrote: > Hello > > I have an expression with Abs applied to the entire denominator: > > 0.5/Abs[(C * R * omega)/(-1 + C * L * omega^2)] > > (Just as an example, the function in Abs could also be another one). How can I transform it to an expression with Abs wrapping the entire Fraction, such as: > Abs[0.5/((C * R * omega)/(-1 + C * L * omega^2))] > > ... and then to: > Abs[(0.5 * (-1 + C * L * omega^2) / (C * R * omega)]] > You can always transform an expression using a transformation, but the onus is then on you to ensure that the transformation is sound: expr= 0.5/Abs[(C * R * omega)/(-1 + C * L * omega^2)] expr/. (num_/;num>0)/Abs[x_] -> Abs[num/x] However, it would seem that Mathematica automatically extracts the factor of 0.5 from Abs. You can only avoid this by using HoldForm to protect the structure of the expression: expr/. (num_/;num>0)/Abs[x_] :> Abs[HoldForm[num]/x] However, beware, this expression is for display only - the HoldForm embedded in the result prevents it being used directly in further calculations. David Bailey http://www.dbaileyconsultancy.co.uk