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Re: Built-In fuctions redefined---How?

• To: mathgroup at smc.vnet.net
• Subject: [mg62624] Re: Built-In fuctions redefined---How?
• From: Peter Pein <petsie at dordos.net>
• Date: Tue, 29 Nov 2005 06:43:40 -0500 (EST)
• References: <dmh92m$8rj$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Virgil Stokes schrieb:
> How can I introduce the following definitions:
> 
>     cx for Cos[x]
>   sx for Sin[x]
>  
> where, the argument x, will always be a single symbol, and then still be 
> able to use the trigonometric identities associated with Sin, Cos; e.g.,
> 
>   cx^2 + sx^2 = 1
> 
> Note, this is not  c x (3 symbol expression); but,  cx (2 symbol 
> expression).
> Why? Because I have some rather large matrices with many elements that 
> contain expressions in Cos and Sin terms that make printing and 
> displaying messy and using the MatrixForm can give truncation in the 
> printed output.
> 
> --V. Stokes
> 
> 
>   

Hi!

Use Format:


In[1]:=
Unprotect[Cos, Sin];
Format[Cos[x_] := "c" <> ToString[x]];
Format[Sin[x_] := "s" <> ToString[x]];

In[4]:=
Expand[(Cos[x] + Sin[t])^3]
Out[4]= "cx"^3 + 3*"cx"^2*"st" + 3*"cx"*"st"^2 + "st"^3

In[5]:= TrigExpand[% /. t -> x]
Out[5]= 1 + 2*"cx"*"sx"

Peter