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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98006] Re: What's going on here (Table-generated lists)?
  • From: dh <dh at metrohm.com>
  • Date: Fri, 27 Mar 2009 05:39:01 -0500 (EST)
  • References: <gqfl2e$ksp$1@smc.vnet.net>


Hi Erik,

your guess is 100% right. Look at: Attributes[Plot] and you will see 

that it has "HoldAll". Therefore, the "Table" will not be evaluated 

before beeing fed to Plot. To evaluate it, simply wrap "Evaluate" around 

the Table.

Daniel



Erik Max Francis wrote:

> 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?

> 




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