[Date Index] [Thread Index] [Author Index]

Re: What's going on here (Table-generated lists)?

• To: mathgroup at smc.vnet.net
• Subject: [mg98031] Re: What's going on here (Table-generated lists)?
• From: Erik Max Francis <max at alcyone.com>
• Date: Sat, 28 Mar 2009 05:43:51 -0500 (EST)
• References: <gqfl2e$ksp$1@smc.vnet.net> <gqiaag$op5$1@smc.vnet.net>

Szabolcs Horv=E1t wrote:
> Erik Max Francis wrote:
>> What is going on here?  Is it something like Plot does a special scan =
of
>> its first argument before Evaluating it, and if it doesn't start out a=
s
>> a List, it concludes that it's all one thing and plots it with the sam=
e
>> color, as opposed to an explicitly provided list of separate colors?
>
> Yes, that is right.
>
> In newer versions of Mathematica, Plot[] is a complicated function that=

> tries to guess whether the argument you provided needs to be evaluated
> symbolically before substituting in numerical values for the plot
> variable, or not.  Of course it cannot always guess right.  In this cas=
e
> it doesn't evaluate the Table before starting the plotting, so it think=
s
> that it'll have only one thing to plot, and thus it uses only one colou=
r.
>
> IMO this is quite silly.  If it is able to plot all five lines, it
> should be able to figure out that it needs five colours ...

Thanks to you and everyone who responded.  I do understand the HoldAll
attribute and why Plot is doing what it's doing.

I fully understand why the HoldAll attribute is generally useful and why
it's used here, but I still don't see why it doesn't make sense for Plot
to recognize a list as an actual list and plot each with a different
color.  Shouldn't it be manually evaluating its argument, then plotting
with different colors if it ends up with a list?

Is there any particular situation where you'd want the current behavior
-- not the HoldAll, but rather the plotting what ends up being a list of
functions with the same color?

--
Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/
  San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
   Always forgive your enemies -- nothing annoys them so much.
    -- Oscar Wilde