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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