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Re: evaluating functions and displaying results numerically

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126183] Re: evaluating functions and displaying results numerically
  • From: Eduardo Fontana <prof.eduardofontana at gmail.com>
  • Date: Tue, 24 Apr 2012 05:30:08 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jmtdec$sjd$1@smc.vnet.net> <4F929712.6060709@KevinMcCann.com> <5BD5FD89-EF13-4752-874A-EB6C13F82D8F@gmail.com>

> My reply to Kevin is now being sent to others who kindly replied to 
this topic. I attached a image file but it was returned by the 
moderator.

> Please read my comments below to Kevin and extensive to others who 
might help. The output file is in a pdf document on google docs on the 
link below.
regards to all
Eduardo

Dear Kevin

> thanks for your reply. I can go along with your explanation, even 
though I havent had this interpretation of results from Mathematica 
before. I never had to use the N option befor. What about my second 
enquire, reproduced below
>>> In another instance, I have a summation of about 1000 terms defined as
>>> a function of 3 arguments. When I use numerical arguments to calculate the summation, instead of
>>> Mathematica calculating a numerical result it generates a symbolic
>>> output with all 1000 terms.
> It doesnt make sense that Mathematica chooses to do the whole thing symbolically. I have made similar calculations before, and Mathematica performed the calculation numerically. I presume that I have enabled some sort of symbolic calculation, but I cannot find where. I am attaching a a link to a pdf file showing a image of the generated result for my function called "Absorption". The other functions are defined prior to the definition of Absorption. I just want to show the type of result generated. Also, If I want to plot my function Absorption relative to one of the arguments, Mathematica just doesnt plot it.
> Best regards
The output image is in the google docs file below
https://docs.google.com/open?id=0Bw08G8QtolpXUDBnQUswdXUyVE0
Eduardo Fontana, PhD
Professor Titular
Dep. de Eletr=F4nica e Sistemas
UFPE - Centro de Tecnologia e Geoci=EAncias
Bloco A, Sala 421 Recife - PE 50.740-550
Skype: edu.fontana
Phones: +5581-21267792, +5511-30424021
http://www.ufpe.br/fontana

>
> 2012/4/21 Kevin J. McCann <kjm at kevinmccann.com>:
>> The output Sin[1] is what is called an "exact", i.e. you gave Mathematica an exact
>> input 1, not 1.0; so, Mathematica returned an exact. If you want a function =
to give
>> a numerical, i.e. machine precision output, do something like this:
>>
>> Sin[1]//N
>>
>> or
>>
>> N[Sin[1]]
>>
>> That is, wrap the result in N[], the number function.
>>
>> Cheers,
>>
>> Kevin
>>
>> On 4/21/2012 12:35 AM, Eduardo Fontana wrote:
>>>
>>> Once in a while a face a problem with Mathematica in which I cannot
>>> get a straightforward numerical output.
>>> I have a function defined in mathematica, I try to evaluate the
>>> function with numerical arguments and mathematica returns a replica of
>>> my function with the same arguments. It must be something I set
>>> without noticing. I cannot get numerical results at all.
>>> In another instance, I have a summation of about 1000 terms defined as
>>> a function of 3 arguments. When I use numerical arguments, instead of
>>> Mathematica calculating a numerical result it generates a symbolic
>>> output with all 1000 terms. Even if a try something very simple such
>>> as
>>> In[1]: Sin[1]
>>> the output is
>>> Out[1]: Sin[1]
>>> Could anyone give me a clue on this?
>>> regards
>>>
>>
>
>
>
> --
> Eduardo Fontana, PhD
> Professor Titular
> Dep. de Eletr=F4nica e Sistemas
> UFPE - Centro de Tecnologia e Geoc=EAncias, Bloco A, Sala 421
> Recife - Pernambuco - 50.740-550
> Fone (Phone): +5581-21267792
> Skype Phone: +5511-30424021
> Skype: edu.fontana
>
> On Apr 21, 2012, at 8:16 AM, Kevin J. McCann wrote:
>
>> The output Sin[1] is what is called an "exact", i.e. you gave Mathematica an exact input 1, not 1.0; so, Mathematica returned an exact. If you want a function to give a numerical, i.e. machine precision output, do something like this:
>>
>> Sin[1]//N
>>
>> or
>>
>> N[Sin[1]]
>>
>> That is, wrap the result in N[], the number function.
>>
>> Cheers,
>>
>> Kevin
>>
>> On 4/21/2012 12:35 AM, Eduardo Fontana wrote:
>>> Once in a while a face a problem with Mathematica in which I cannot
>>> get a straightforward numerical output.
>>> I have a function defined in mathematica, I try to evaluate the
>>> function with numerical arguments and mathematica returns a replica of
>>> my function with the same arguments. It must be something I set
>>> without noticing. I cannot get numerical results at all.
>>> In another instance, I have a summation of about 1000 terms defined as
>>> a function of 3 arguments. When I use numerical arguments, instead of
>>> Mathematica calculating a numerical result it generates a symbolic
>>> output with all 1000 terms. Even if a try something very simple such
>>> as
>>> In[1]: Sin[1]
>>> the output is
>>> Out[1]: Sin[1]
>>> Could anyone give me a clue on this?
>>> regards
>>>
>
> Eduardo Fontana, PhD
> Professor Titular
> Dep. de Eletr=F4nica e Sistemas
> UFPE - Centro de Tecnologia e Geoci=EAncias
> Bloco A, Sala 421, Recife - PE 50740-550
>
>
>


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