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Re: Not all points plot on my graph...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105222] Re: Not all points plot on my graph...
  • From: Helen Read <hpr at together.net>
  • Date: Wed, 25 Nov 2009 02:29:59 -0500 (EST)
  • References: <200911231149.GAA21721@smc.vnet.net> <hegej6$18h$1@smc.vnet.net>

Tomas Garza wrote:
> 
> BTW, I would use SetDelayed (:=) instead of Set (=) in the definition of f.
>>
>> f[x_] = (x + 2)^(2/3)

That's a matter of taste, I think. I have for many years taught my 
students to use Set when defining garden variety functions. An advantage 
of this is that the function is immediately evaluated and you get 
output, which allows students to catch many errors. For example, suppose 
they left off the parentheses in the function quoted above, and entered 
(x+2)^2/3 . They will immediately see their mistake if they pay the 
slightest attention to the output, and can fix it immediately. Using 
SetDelayed, it's the rare student who will figure out that they entered 
the function incorrectly. This year I have noticed more of this type of 
error, because the students learned to define functions by using the 
Define Function button on the Classroom Assistant palette, which uses 
SetDelayed, and most of them have continued to use SetDelayed after they 
stopped relying on the palette. (I have showed the students that can 
check the definition of their function by typing in f[x] and evaluating, 
but nobody seems to think of it even when it is clear that something 
isn't right.)

There are of course times when we need SetDelayed, and we discuss it in 
class when it comes up.

--
Helen Read
University of Vermont




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