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Re: Rule replacement doesn't work after NDSolve?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg124004] Re: Rule replacement doesn't work after NDSolve?
*From*: Bill Rowe <readnews at sbcglobal.net>
*Date*: Thu, 5 Jan 2012 05:56:05 -0500 (EST)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
On 1/4/12 at 5:03 AM, g.crlsn at gmail.com (gac) wrote:
>Thanks very much for the reply. Your suggestion works as you say,
>but I'm still confused. I thought that the replacement is for the
>function, not the arguments.
Replacement rules are not limited to either functions or
arguments. For example, I can do:
In[3]:= Cos[y] /. Cos -> Sin
Out[3]= Sin[y]
replacing the Cos function with Sin or
In[4]:= Cos[y] /. y -> 2 x
Out[4]= Cos[2*x]
replacing the argument y with 2 x
The thing to keep in mind with replacement rules is a litteral
match is made between the FullForm of the expression you want to
operate on and the left hand side of the replacement rule. For
example, this does nothing:
In[5]:= -2 I /. I -> -I
Out[5]= -2*I
since
In[6]:= FullForm[-2 I]
Out[6]//FullForm= Complex[0,-2]
and there is nothing to match the left hand side of the
replacement rule
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