Erf funcion

*To*: mathgroup at smc.vnet.net*Subject*: [mg123947] Erf funcion*From*: Vicent <vginer at gmail.com>*Date*: Sun, 1 Jan 2012 02:29:27 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Hello. I have an expression that depends on the Cumulative Distribution Function (CDF) of a Normal Variable with mean = 0 and standard deviation = 1. When I perform operations and/or derivatives with/for that function with Mathematica, I get expressions involving Erf function, as the CDF function of a Normal distributed variable and Erf (error function) are closely related. Concretely, FiX[x] == (1/2)*(1 + Erf[x/Sqrt[2]]) and thus Erf[x] == 2*FiX[x*Sqrt[2]] - 1 where FiX stands for the previously mentioned CDF, I mean: X = NormalDistribution[0, 1] FiX[x_] := CDF[X, x] Is there a quick way to ask Mathematica not to use Erf but always let the results as a function of FI[x]?? The expressions I get as a result of my computations are larger than this short example: 3 (2^(7/2 - 2 (k + t))) Cp ( E^(-d^2 - (36 Cp^2)/lambda^2)) ((Erf[(-d + (6 Cp)/lambda)/Sqrt[2]] + Erf[(6 Cp + d lambda)/(Sqrt[2] lambda)])^k) where "Cp", "k", "t", "d" and "lambda" are parameters or arguments that I want to keep as "generic". So, how can I "translate" expressions such as the last one into "FiX mode"? Or, better, how can I prevent Mathematica to reduce everything to "Erf mode"?? I hope my question is clear enough... :) Thank you very much in advance for your answers. And have a good new year! -- vicent dooid.com/vicent

**Follow-Ups**:**Re: Erf funcion***From:*DrMajorBob <btreat1@austin.rr.com>

**Re: Erf funcion***From:*Bob Hanlon <hanlonr357@gmail.com>

**Re: Erf funcion***From:*DrMajorBob <btreat1@austin.rr.com>