![[Graphics:Images/index_gr_1.gif]](Images/index_gr_1.gif){kind=small}
e ![[Graphics:Images/index_gr_2.gif]](Images/index_gr_2.gif){kind=small}
como forma de melhorar a interface da função join. O símbolo "pinf" viria a ser aceito, mas Rick trocou minf (que escrevi pensando em minus infinity) por ninf (de negative infinity).
Aos entusiastas do Winplot, apresento abaixo parte da longa correspondência eletrônica que mantive com Richard Parris ("Rick") sobre o uso de funções características no seu software. Exceto pelas omissões indicadas, os e-mails foram transcritos sem qualquer alteração. O leitor saberá identificar os erros e lapsos contidos nos originais, inevitáveis em textos desse tipo.
Minha proposta para a inclusão de chi se deu durante o período em que Rick trabalhava no código do novo Winplot. Por aquela época, trocávamos e-mails diariamente, sobre os mais variados temas. Numa certa altura, sugeri-lhe que introduzisse símbolos para e como forma de melhorar a interface da função join. O símbolo "pinf" viria a ser aceito, mas Rick trocou minf (que escrevi pensando em minus infinity) por ninf (de negative infinity).
----- Original Message -----
From: "Carlos César" <carlos.cesar@task.com.br>
To: "Richard L. Parris" <rparris@exeter.edu>
Sent:
Saturday, February 10, 2001 2:37 PM
Subject: A symbol for infinity
A suggestion for your new version:
Talking about the JOIN operator, I note that although the syntax is quite
clear for ME, it is found difficult to get used to by some TEACHERS
here. A
possible *fix* would be the inclusion of a symbol for (simulating)
INFINITY.
Thus we would have
JOIN(minf|f(x)|a,g(x)|b,h(x)|pinf)
intead of
(or along with)
JOIN(f(x)|a,g(x)|b,h(x))
(Above, minf stands for minus infinity and pinf for plus
infinity.) A think
the above notation should be allowed as an option.)
Carlos
No e-mail transcrito abaixo (com omissões), faço a primeira sugestão sobre a função chi.
----- Original Message -----
From: "Carlos César" <carlos.cesar@task.com.br>
To: "Richard L. Parris" <rparris@exeter.edu>
Sent:
Saturday, February 10, 2001 10:39 PM
Subject: Infiniy and Heaviside
(...)
I have another reason for the inclusion of INFINITY. I note that engineers
(following the great Oliver
Heaviside) prefer to deal with the so-called
Heaviside function.
Mathematicians, on the other hand, like to see
everything (in this context) in terms of CHARACTERISTIC functions (a.k.a
INDICATORS). At least, I myself use such functions a lot. Now, suppose that
we had in Winplot's library a function like
chi(x,a,b) = 1 if x is in [a,b] and 0 otherwise.
Then
Heaviside(x) = chi(x,0, +infinity)
Of course, it is possible to define chi using hvs. But I consider the chi
function infinitely more useful, ubiquitous and flexible.
(...)
Cinco dias depois, após driblar alguns problemas de compilação, Rick implementa a função chi.
----- Original Message -----
From: "Richard L. Parris" <rparris@exeter.edu>
To: <rparris>
Cc: <carlos.cesar@task.com.br>
Sent: Thursday, February 15, 2001 12:26 PM
Subject: Re: chi again
Carlos:
Have written chi(a,b,x) into my code for the new Winplot. It was a bit of a
problem, because chi is a ternary function, and I was not able to build it
up easily using my binary approach to parsing. (By way of contrast, the join
construction is simple, because each comma can be made into a binary
operator). So I was tempted to just let the heaviside function do the job,
but the challenge was too much to resist.
By the way, which would be better, chi(a,b,x) or chi(a,x,b)?
It should be ready in a few days.
Rick
Observem que no meu e-mail escrevi "chi(x,a,b)", mas Rick preferiu ficar com
"chi(a,b,x)" argumentando que era a notação mais natural ![[Graphics:Images/index_gr_3.gif]](Images/index_gr_3.gif){kind=small}
com o que concordei plenamente.
No e-mail abaixo, Rick anuncia o lançamento do seu novo Winplot, já com a função chi definitivamente incorporada.
----- Original Message -----
From: "Richard L. Parris" <rparris@exeter.edu>
To: "Carlos César de Araújo" <carlos.cesar@task.com.br>
Sent: Friday, March 02, 2001 2:11 PM
Subject: wp32
Cear:
I uploaded Winplot for Windows 98 today. I look forward to your feedback.
Rick
© Carlos César de Araújo - Sábado, 25 de Maio de 2002