[Maxima-bugs] [ maxima-Bugs-3459556 ] draw3d of z=0: there is no surface in a draw3d range

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Bugs item #3459556, was opened at 2011-12-14 09:11
Message generated for change (Comment added) made by riotorto
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Edd Barrett (vext0101)
Assigned to: Nobody/Anonymous (nobody)
Summary: draw3d of z=0: there is no surface in a draw3d range

Initial Comment:
Consider this function:

convex_env(u_l, u_h, v_l, v_h, z_l, z_h) :=

wxdraw3d(
  xrange = [u_l, u_h],
  yrange = [v_l, v_h],
  zrange = [z_l, z_h],

    implicit(
      z=((v_l*v) - (u_l*u) + (u_l*v_l)),
      u, u_l, u_h, v, v_l, v_h, z, z_l, z_h
    )
)$

Most applications of this function yield a surface, however, sometimes the result is a single point and maxima bails out. Eg: 

convex_env(0, 2, 0, 2, 0, 2);

gives:

draw3d (implicit): no surface within these ranges.

Infact it is the same as plotting:
implicit(
      z=0,
      u, u_l, u_h, v, v_l, v_h, z, z_l, z_h
    )

Is z=0 not a surface within z=[0, 2]?

I get the same when drawing z=0.1, but not for z=0.2.

Is this correct ?



----------------------------------------------------------------------

>Comment By: Mario Rodriguez Riotorto (riotorto)
Date: 2011-12-15 00:17

Message:
Hello,

I'll take a look at this.

In the meantime, you can consider if the following workaround, or something
similar, fits your needs:

convex_env(ul, uh, vl, vh, zl, zh) :=

wxdraw3d(
  xrange = [ul, uh],
  yrange = [vl, vh],
  zrange = [zl, zh],

    implicit(
      z=((vl*v) - (ul*u) + (ul*vl)),
      u, ul-0.1, uh+0.1, v ,vl-0.1, vh+0.1, z, zl-0.1, zh+0.1
    )
)$

--
Mario

----------------------------------------------------------------------

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