Re: Thread function now working as expected

*To*: mathgroup at smc.vnet.net*Subject*: [mg74616] Re: Thread function now working as expected*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Wed, 28 Mar 2007 01:45:29 -0500 (EST)*Organization*: The Open University, Milton Keynes, UK*References*: <euan64$do9$1@smc.vnet.net>

siewsk at bp.com wrote: > I cannot get the Thread function to work on In[3] and I > am forced to do it manually in In[4] > > Does anyone has any idea why In[3] is not working as I expected? > > In[1]:= eqn1 = Sqrt[1 + 196*x^4] == 12*x - 1 - 14*x^2 > Out[1]= > 4 2 > Sqrt[1 + 196 x ] == -1 + 12 x - 14 x > > > In[2]:= eqn2 = Thread[(#1^2 & )[eqn1], Equal] > Out[2]= > 4 2 2 > 1 + 196 x == (-1 + 12 x - 14 x ) > > > In[3]:= dummy = Thread[Expand[eqn2], Equal] > Out[3]= > 4 2 2 > 1 + 196 x == (-1 + 12 x - 14 x ) [snip] Expand is evaluated before Thread is applied. Use a dummy head and a transformation rule. For instance, In[1]:= eqn1 = Sqrt[1 + 196*x^4] == 12*x - 1 - 14*x^2; eqn2 = Thread[(#1^2 & )[eqn1], Equal]; dummy = Thread[ed[eqn2], Equal] /. ed -> Expand Out[3]= 4 2 3 4 1 + 196 x == 1 - 24 x + 172 x - 336 x + 196 x Regards, Jean-Marc