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Re: Matrices as operators

  • To: mathgroup at
  • Subject: [mg123217] Re: Matrices as operators
  • From: Chris Young <cy56 at>
  • Date: Sun, 27 Nov 2011 04:12:40 -0500 (EST)
  • Delivered-to:
  • References: <jaal4e$12d$> <jaqjn9$oj7$>

On 2011-11-26 11:48:57 +0000, Ray Koopman said:

> This won't try to interpret a number as a function:
> In[1]:= op[mat_, t_] := Map[If[NumericQ@#, #, #@t] &, mat, {-1}]
> In[2]:= op[{{Sin, Cos}, Tan, {Cos, 0, 1}}, t]
> Out[2]= {{Sin[t], Cos[t]}, Tan[t], {Cos[t], 0, 1}}

Just discovered a notation I like a lot for pure functions: the 
standard "tee-arrow" notation can be used wherever a pure function can 
be used! This is explained on the Help page for "Function", in the 
"More Information" section.

Function[x, body]


# body &

can always be converted to the "tee-arrow" form, I believe.

The tee-arrow is entered by typing Escape fn Escape.

So the matrix-operator function Ix had earlier,

op[arr_, t_] :=
  If[! (NumericQ[#] || StringQ[#]),
    ] &,

would become (in input form)

op[arr_, t_] :=
  x \[Function] If[! (NumericQ[x] \[Or] StringQ[x]), x[t], x],

Applying this to the test array
arr = {{Sin, Cos}, Tan, {Cos, Cos[Cos], 1}, "string"},
we get

In[100]:= op2[arr, t]

Out[100]= {{Sin[t], Cos[t]}, Tan[t], {Cos[t], Cos[Cos[t]], 1}, "string"}

I can't type out the tee-arrow in text form, but it goes where 
"\[Function]" appears above.

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