[Maxima-bugs] [ maxima-Bugs-701677 ] plot2d evaluates outside range

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Bugs item #701677, was opened at 2003-03-11 12:18
Message generated for change (Comment added) made by rtoy
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=104933&aid=701677&group_id=4933

Category: Lisp Core
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Stavros Macrakis (macrakis)
Assigned to: Raymond Toy (rtoy)
Summary: plot2d evaluates outside range

Initial Comment:
plot2d evaluates the function being plotted outside the 
given range.

Try:

f(x):= if (x>1) then 0 else x^2$

plot2d(f,[x,0,1])

The plot shows the function dropping to 0 at x=1+eps.

This is bad for three reasons:

1) I explicitly asked for the range [0,1].  I do not want to 
see the behavior for x>1.

2) I don't want the y-range to be distorted by an outlier at 
x=1+eps.

3) the function may not be well-defined, and may cause 
errors, outside the range I gave.  (This is how I 
discovered the issue.)

Plot2d also evaluates the function at twice as many 
values as it uses (to check for smoothness) -- I'd think 
we could do better than that, but maybe not.

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>Comment By: Raymond Toy (rtoy)
Date: 2003-05-25 13:43

Message:
Logged In: YES 
user_id=28849

Should be fixed now.

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Comment By: Raymond Toy (rtoy)
Date: 2003-04-03 13:25

Message:
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user_id=28849

I agree.  This is very annoying.

I think the reason is due to round off and the way extra
samples are taken.

I have a fix for this so we don't go outside the range, and
every computed point is used in the plot instead of throwing
away half the points.

Needs work.

I think we should give up on being smart.

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