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Re: What's going on here (Table-generated lists)?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg97975] Re: [mg97956] What's going on here (Table-generated lists)?
*From*: "David Park" <djmpark at comcast.net>
*Date*: Fri, 27 Mar 2009 05:33:04 -0500 (EST)
*References*: <1959064.1238066744184.JavaMail.root@m02>
It is because Plot has the Attribute HoldAll. It sees only one argument so
it uses only one color. (But this is something of a feature!)
The following works because the first argument is evaluated before the Plot
algorithm goes into action.
Plot[Evaluate@Table[k x, {k, 1, 5}], {x, -1, 1}]
Or
data = Table[k x, {k, 1, 5}]
{x, 2 x, 3 x, 4 x, 5 x}
Plot[data, {x, -1, 1}]
But the following does not work because the Table is not evaluated first.
data := Table[k x, {k, 1, 5}]
Plot[data, {x, -1, 1}]
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/
From: Erik Max Francis [mailto:max at alcyone.com]
I'm seeing a difference in behavior with Plot in conjunction with Table,
and I'm rather confused at the reason. If I use Plot to plot a list
of functions, it works as expected, and I get a plot with each function
in its own color:
Plot[{x, 2 x, 3 x, 4 x, 5 x}, {x, -1, 1}]
If I use Table, then this doesn't work the same way -- the five lines
are all plotted with the same color:
Plot[Table[k x, {k, 1, 5}], {x, -1, 1}]
I verified that the both objects created have a Head of List, so I don't
see anything obviously different about them.
Here's what confuses me more: If I generate the table separately and
then use that as a result in a later evaluation in the Plot, then I get
the colors back:
In[25]:= Table[k x, {k, 1, 5}]
Out[25]= {x, 2 x, 3 x, 4 x, 5 x}
In[26]:= Plot[%, {x, -1, 1}]
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 as
a List, it concludes that it's all one thing and plots it with the same
color, as opposed to an explicitly provided list of separate colors?
--
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
In this world, nothing is certain but death and taxes.
-- Benjamin Franklin
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