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MathGroup Archive 1993

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buggish feature of Plot ???

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: buggish feature of Plot ???
  • From: wmm at chem.wayne.edu (Martin McClain)
  • Date: Tue, 2 Mar 93 13:29:47 EST

The Plot operator seems to suffer a lot from its HoldAll attribute. 
Blachman gives as example (p.216) where it draws, without warning, a plot
that seems plainly wrong to humans: 
                s = 2x/(10x+5);
                Plot[Numerator[s],{x,0,5}];
There are other less disturbing examples where it fails to produce a plot
from a command that seems quite clear. The fix in all cases is the same;
namely, an Evaluate which overrides the HoldAll attribute of Plot:
                 Plot[Evaluate[Numerator[s]],{x,0,5}].
My question:  Why does Plot have the HoldAll attribute?  What would happen
if I unprotected Plot and took HoldAll away permanently?  Can anyone give
an example of misbehaviour if this is done ?






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