Re: ProductLog[-Pi/2]

*To*: mathgroup at smc.vnet.net*Subject*: [mg44182] Re: ProductLog[-Pi/2]*From*: "Christos Argyropoulos M.D." <argchris at otenet.gr>*Date*: Sat, 25 Oct 2003 06:26:35 -0400 (EDT)*References*: <bnapg7$4lk$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, Actually this is the expected behaviour; You entered an exact number in the ProductLog function, and you get back an exact number (i.e. ProductLog[Pi/2]) Mathematica will keep this special function result in this exact format, unless requested to return a numeric result. Try ProductLog[1], will return the same thing. If getting back I Pi/2 is crucial to your application try the following: In[1]:= ProductLog[-Pi/2] ProductLog[N[-Pi/2]]//Chop Unprotect[ProductLog]; ProductLog[-Pi/2]= I Pi/2; Protect[ProductLog]; ProductLog[-Pi/2] Out[1]= \!\(ProductLog[\(-\(\[Pi]\/2\)\)]\) Out[2]= 1.5708 \[ImaginaryI] Out[6]= \!\(\(\[ImaginaryI]\ \[Pi]\)\/2\) Best Regards Christos Argyropoulos MD Athens, Greece ----- Original Message ----- From: "Jean-Claude Poujade" <poujadej at yahoo.fr> To: mathgroup at smc.vnet.net Subject: [mg44182] ProductLog[-Pi/2] > ProductLog[-Pi/2] should return I Pi/2 but doesn't... > > In[1] := w E^w /. w -> I Pi/2 > Out[1] = -Pi/2 > > In[2] := ProductLog[-Pi/2] // FullSimplify > Out[2] = ProductLog[-Pi/2] > > In[3] := ProductLog[-Pi/2] // N // Chop > Out[3] = 1.5708 I > > Could someone explain ? (I use Mathematica 4.1) > > --- > jcp >