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Re: Re: Re: Putting an If in my function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg101191] Re: [mg101093] Re: [mg101073] Re: Putting an If in my function
  • From: DrMajorBob <btreat1 at austin.rr.com>
  • Date: Fri, 26 Jun 2009 06:51:17 -0400 (EDT)
  • References: <h1neun$8rk$1@smc.vnet.net> <200906241029.GAA22903@smc.vnet.net>
  • Reply-to: drmajorbob at bigfoot.com

Set (=) is evaluated immediately, but the condition (/;g == w) can't be  
evaluated until g and w are known.

Bobby

On Wed, 24 Jun 2009 05:29:07 -0500, Porscha Louise McRobbie  
<pmcrobbi at umich.edu> wrote:

> Hi,
>
> I'm also interested in adding a special case to a function. Using
> what's written below works fine:
>
> myFun[a_, g_, f_, x_, d_, w_] := d + a f x /; g == w
>
> But why doesn't the same work when the myFun is defined using "="
> instead of":="?  i.e.,
>
> myFun[a_, g_, f_, x_, d_, w_] = (d + a f x) /; g == w
> ln[5]:=myFun[a, w, f, x, d, w]
> Out[5]=d + a f x /; w == w
>
> Thanks,
> Porscha
>
>
> Quoting "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>:
>
>> Dear lobotomy,
>>
>> "Nomen est omen", the old Romans used to say. And they were often
>> right.
>>
>> I'm not sure what you are trying to do here, with your function in an
>> unneccessary, overly complex, pure function notation. Why not write:
>>
>> myFun[a_, g_, f_, x_, d_, w_] := d (1 + (E^g - E^w)/f)^(f x) + (a (-1
>> + (1 + (E^g - E^w)/f)^(f x)) f)/( E^g - E^w)
>>
>> which is much more readable (at least in Mathematica)?
>>
>> In[31]:= Limit[myFun[a, g, f, x, d, w], g -> w]
>>
>> Out[31]= d + a f x
>>
>> You use the undefined 'n' in d + a n. I guess this must be f x...
>>
>> You can add a definition for myFun for this special case like this (no
>> If[ ] necessary):
>>
>> myFun[a_, g_, f_, x_, d_, w_] := d + a f x /; g == w
>>
>> In[36]:= myFun[a, w, f, x, d, w]
>>
>> Out[36]= d + a f x
>>
>> If you want to use an If in the definition this would be something
>> like:
>>
>> myFun[a_, g_, f_, x_, d_, w_] := If[g===w, d (1 + (E^g - E^w)/f)^(=
> f=
>>  x)
>> + (a (-1 + (1 + (E^g - E^w)/f)^(f x)) f)/( E^g - E^w),d + a f x]
>>
>> Cheers -- Sjoerd
>>
>> On Jun 22, 10:21 am, Lobotomy <labb... at gmail.com> wrote:
>>> Hi, this is my function
>>>
>>> #5 (1 + ((E^#2 - 1) - (E^#6 -
>>>             1))/#3)^(#3*#4) + (#1*((1 + (((E^#2 - 1) - (E^#6 =
>> -
>>>                  1))/#3))^(#3*#4) -
>>>         1))/(((E^#2 - 1) - (E^#6 - 1))/#3) &[a, g, f, x, d, w]
>>>
>>> in the case when w==g the denominator equals zero.
>>>
>>> in this case i would like to rewrite the formula above to the much
>>> simpler
>>> d+a*n. How is this done? I've tried
>>>
>>> If[w == g, % = d + a*n], but this is not working. Another thing is
>>> where to put the "If"
>>
>>
>>
>>
>>
>
>



-- 
DrMajorBob at bigfoot.com


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