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Re: Matrices as operators

  • To: mathgroup at smc.vnet.net
  • Subject: [mg123216] Re: Matrices as operators
  • From: Chris Young <cy56 at comcast.net>
  • Date: Sun, 27 Nov 2011 04:12:29 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jaal4e$12d$1@smc.vnet.net> <jafu4b$ro7$1@smc.vnet.net> <janol1$aqb$1@smc.vnet.net> <jaqe26$nhv$1@smc.vnet.net>

Checking out the Help for Map, I found that you could put tests in with 
an If[ ] that was acting as a pure function.  I think the following 
will always do what I want. Should be much faster than using While 
loops, too.

op2[arr_, t_] :=
Map[
 If[! (NumericQ[#] || StringQ[#]),
  #[t],
  #
  ] &,
 arr,
 {-1}
 ]


In[38]:= op2[{{Sin, 3 E, Cos}, Tan, {Cos, Cos[Cos], 1}, "string"}, t]

Out[38]= {{Sin[t], 3 E, Cos[t]}, Tan[t], {Cos[t], Cos[Cos[t]], 1}, "string"}

The {-1} tells Map to only apply the change to the ends of the 
expression tree. The If[ ] filters out numbers and strings, which are 
not valid function names.

Some more tests would have to be added if you wanted this to work for 
indexed functions such as f[k][x].

Seems like this is probably the fastest way to accomplish what I want, 
since it's all built-in. Amazing!

Chris Young
cy56 at comcast.net




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