*To*: mathgroup@smc.vnet.net*Subject*: [mg10636] Re: [mg10492] Re[a + I b] = a*From*: David Withoff <withoff@wolfram.com>*Date*: Tue, 27 Jan 1998 03:10:01 -0500

> how can I tell mathematica that the variable a and b is real, so that > Re[a+ I b] results to a? ComplexExpand assumes that a and b are real unless you tell it otherwise. In[2]:= ?ComplexExpand ComplexExpand[expr] expands expr assuming that all variables are real. ComplexExpand[expr, {x1, x2, ... }] expands expr assuming that variables matching any of the xi are complex. In[3]:= ComplexExpand[ Re[a + I b] ] Out[3]= a > or: n a integer number and Sin[n x] results to 0? > > I am using mathematica 2.2 Algorithmically, this is a much harder (and largely unsolved) problem. If your needs are not too elaborate, though, you may be able to program it yourself, as in In[4]:= Unprotect[Sin] ; In[5]:= Sin[p_ Pi] := 0 /; IntegerQ[p] In[6]:= Protect[Sin] ; In[7]:= IntegerQ[n] ^= True ; In[8]:= Sin[n Pi] Out[8]= 0 Dave Withoff Wolfram Research