Re: Converting a number back to a symbol?

*To*: mathgroup at smc.vnet.net*Subject*: [mg82900] Re: Converting a number back to a symbol?*From*: Szabolcs Horvát <szhorvat at gmail.com>*Date*: Fri, 2 Nov 2007 05:04:48 -0500 (EST)*References*: <fgenct$fsd$1@smc.vnet.net>

AES wrote: > If we have an expression containing integer powers of the symbol u0 and > we know that u0's numerical value is (or at least eventually will be) u0 > = Pi/2, we know what happens if we write > > expr /. {u0 -> Pi/2} > > But what about the reverse case: we have an expression containing > various integer powers of Pi, and we want to replace all the explicitly > appearing Pi's by 2 u0. Writing > > expr /. {Pi-> 2 u0} > > doesn't seem to do it. > > Is there a way? > Can you give a full, evaluatable example? It works for me: In[1]:= Plus@@(Pi^Range[3]) Out[1]= Pi + Pi^2 + Pi^3 In[2]:= % /. Pi->2u0 Out[2]= 2 u0 + 4 u0^2 + 8 u0^3 -- Szabolcs