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MathGroup Archive 2006

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Re: Function defined with If

  • To: mathgroup at smc.vnet.net
  • Subject: [mg71396] Re: Function defined with If
  • From: Bill Rowe <readnewsciv at sbcglobal.net>
  • Date: Thu, 16 Nov 2006 00:54:22 -0500 (EST)

On 11/15/06 at 6:43 AM, julian.aguirre at ehu.es (Julian Aguirre) wrote:

>I am trying to define a function of the variables x, y through other
>quantities depending on x and y and the function If. A minimal
>example is

>In[1]:=
>a = x;
>b = y;
>f[ x_, y_ ] = If[ a < b, a, b ]
>Out[3]=
>If[ x < y, a, b ]

>How can I force Mathematica to return If[ x < y, x, y ], as I
>thought it would?

Simply define the function appropriately. There is little point 
in defining a function that takes arguments named x, y as you 
done above when none of the named arguments appear on the right 
hand side.

The following definition for f will do what you want provided x 
and y do not have defined values

f[x_, y_]:=If[x<y,x,y]

Note, x,y appear on both sides and the usage of SetDelayed ":=" 
rather than Set "=". In general, you will want to define 
functions with SetDelayed not Set.
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