Re: Converting a number back to a symbol?

*To*: mathgroup at smc.vnet.net*Subject*: [mg82918] Re: Converting a number back to a symbol?*From*: "Dr. Wolfgang Hintze" <weh at snafu.de>*Date*: Sat, 3 Nov 2007 03:27:34 -0500 (EST)*References*: <fgenct$fsd$1@smc.vnet.net>*Reply-to*: "Dr. Wolfgang Hintze" <weh at snafu.de>

"AES" <siegman at stanford.edu> schrieb im Newsbeitrag news:fgenct$fsd$1 at smc.vnet.net... > 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? > I don't see the problem: Here's an example (Pi is always being entered from the keyboard using the sequence ESC p ESC) In[1]:= a = 2 \[Pi] (* entered with ESC p ESC *) Out[1]= 2*Pi In[4]:= a /. {Pi -> pu} Out[4]= 2*pu Cheers, Wolfgang