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Re: Pi vs its decimal approximation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113178] Re: Pi vs its decimal approximation
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 16 Oct 2010 13:13:36 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

You did not include a space between the Pi and x so they make a single symbol which is undefined. In the numeric case the multiplication is implied so it works as expected.


Bob Hanlon

---- John Accardi <accardi at accardi.com> wrote: 

=============
  Thanks in advance for any insights ...

In my notebook below, why doesn't cosine2 graph?
When I replace the symbol for
Pi with the decimal approx in the definition of cosine3,
it graphs correctly. .  Why does Mathematica not interpret
Pi correctly in the first definition of cosine2?


In[29]:= cosine2:= 2/3 Cos[2\[Pi]x - \[Pi]/2 ] +1

In[30]:= yline:=1

In[31]:= Plot[Tooltip[{cosine2, yline}], {x, 0, 1.5},
  Ticks -> {{0, .1, .2, .3, .4, .5, .6, .7, .8, .9, 1.0, 1.1, 1.2, 1.3, 
1.4,
     1.5}, Automatic}]

The plot that appears here only shows the y=1 line, not the cosine2.



But now I replace the symbol Pi with a decimal approximation in the
definition of cosine3 .. and it graphs correctly.

In[20]:= cosine3:=  2/3 Cos[2(3.141592653589793`)x- \[Pi]/2 ] +1

In[14]:= yline:=1

In[15]:= Plot[Tooltip[{cosine3, yline}], {x, 0, 1.5},
  Ticks -> {{0, .1, .2, .3, .4, .5, .6, .7, .8, .9, 1.0, 1.1, 1.2, 1.3, 
1.4,
     1.5}, Automatic}]

The plot that shows here is correct. It contains both y=1 and
cosine3.  The only difference is the use of Pi vs 3.14159265...
(I inputted Pi using the Greek letter on the Classroom Assistant.)


*.nb file here:

http://www.accardi.com/PiQuery.nb


Gianni




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