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Re: Re: Suppressing display of LogPlots

• To: mathgroup at smc.vnet.net
• Subject: [mg22649] Re: [mg22614] Re: Suppressing display of LogPlots
• From: Hartmut Wolf <hwolf at debis.com>
• Date: Thu, 16 Mar 2000 09:11:07 -0500 (EST)
• Organization: debis Systemhaus
• References: <8aejj2$3aj@smc.vnet.net> <200003150346.WAA01854@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Dr Dan, 
dear Allan,


if you observe

In[11]:= << "Graphics`Graphics`"

In[12]:= g2 = LogLinearPlot[Sin[x], {x, 0, 3*Pi}]
 -- Graphics deleted --
Out[12]= Graphics[]

In[13]:= Cases[g2, _[DisplayFunction, _], -1]

Out[13]= {DisplayFunction -> (Display[$Display, #1] & ), 
  DisplayFunction :> Identity}

You'll see that second ominous DisplayFunction :> Identity, and the
first Option DisplayFunction -> (Display[$Display, #1] & ) that reflects
the value of the $DisplayFunction global variable at the time of the
execution of In[12].


If you follow standard procedures to create the Graphics with Plot but
without showing you'll get 

In[14]:= g2a = LogLinearPlot[Sin[x], {x, 0, 3*Pi}, 
   DisplayFunction -> Identity]

Out[14]= Graphics[]

In[15]:= Cases[g2a, _[DisplayFunction, _], -1]
 
Out[15]= {DisplayFunction -> Identity, DisplayFunction :> 
   Identity}

In[16]:= Show[g2a, DisplayFunction -> $DisplayFunction]
 -- Graphics deleted --
Out[16]= Graphics[]
 
In[17]:= Cases[%, _[DisplayFunction, _], -1]

Out[17]= {DisplayFunction -> (Display[$Display, #1] & ), 
  DisplayFunction :> Identity}


Compare this with the built-in

In[20]:= g1 = Plot[Sin[x], {x, 0, 3*Pi}, DisplayFunction -> 
    Identity]

Out[20]= Graphics[]

In[21]:= Cases[g1, _[DisplayFunction, _], -1]

Out[21]= {DisplayFunction :> Identity}

In[22]:= Show[g1, DisplayFunction -> $DisplayFunction]
 -- Graphics deleted --
Out[22]= Graphics[]

In[23]:= Cases[%, _[DisplayFunction, _], -1]

Out[23]= {DisplayFunction -> (Display[$Display, #1] & ), 
  DisplayFunction :> Identity}


So I see no point in neither changing the packages, nor cleaning up.
Block-ing the global variables is risky anyways, doing so might be a
handy trick, but if something goes wrong, than the trick is the bug;
exempli causa:

In[24]:= Block[{$DisplayFunction}, 
  g2x = LogLinearPlot[Sin[x], {x, 0, 3*Pi}]; ]

In[25]:= g2x
 -- believe it or not, Graphics was here --
Out[182]= Graphics[]

In[26]:= Cases[g2x, _[DisplayFunction, _], -1]
 -- again, Graphics was here --
Out[183]= {DisplayFunction -> (Display[$Display, #1] & ), 
  DisplayFunction :> Identity}


Let's finally compare

In[27]:= g2 === g2x
 -- again, Graphics was here (once only!) --
Out[27]= True


So not all is perceptible to us!


Kind regards, Hartmut

• References:
  • Re: Suppressing display of LogPlots
    • From: "Allan Hayes" <hay@haystack.demon.co.uk>