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Re: set option flag in function definition

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  • Subject: [mg128160] Re: set option flag in function definition
  • From: Murray Eisenberg <murray at>
  • Date: Wed, 19 Sep 2012 05:00:19 -0400 (EDT)
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On Sep 18, 2012, at 3:41 AM, Joug Raw <jougraw at> wrote:

> ...I want to have a function that executes certain operation when I chose the
> corresponding option flag.
> For example,
> a function called "f"
> when I call it like f[arg1,arg2,arg3, optionX]
> it executes command
> arg1/arg2+arg3
> If I call it like f[arg1,arg2,arg3,optionY]
> it executes command
> arg1*arg2-arg3
> If I call it like f[arg1,arg2,arg3,optionSomethingElse]
> it returns me
> "No appropriate option flag was found. Please indicate correct options"
> ...I am wondering if I can do
> the same in Mathematica easily?

Yes, it can be done very easily in Mathematica:

  f[a_, b_, c_, method -> "one"] := a/b+c
  f[a_, b_, c_, method -> "two"] := a b-c
  f[a_, b_, c_, method -> _] := "No relevant value for 'method' found"
  f[a_, b_, c_, opt_ -> _] := "I don't understand this option"

(I shortened argument names; the option name "method" I used is quite arbitrary.)

The key to the above is that Mathematica always uses a more specific rule before it uses a more general one.

If, though, you want a single expression for defining the function f, then yes that's also possible but more complicated; you cold use, e.g., FilterRules.

Murray Eisenberg                                     
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