#20461: Fixes for copying a MIP and its variables
-----------------------------+------------------------
       Reporter:  mkoeppe    |        Owner:
           Type:  defect     |       Status:  new
       Priority:  major      |    Milestone:  sage-7.2
      Component:  numerical  |   Resolution:
       Keywords:  lp         |    Merged in:
        Authors:             |    Reviewers:
Report Upstream:  N/A        |  Work issues:
         Branch:             |       Commit:
   Dependencies:             |     Stopgaps:
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Comment (by mkoeppe):

 Actually I spoke too fast, it seems that `gen()` does not do anything
 useful.

 {{{
 sage: mip = MixedIntegerLinearProgram(solver='GLPK')
 sage: mip.gen(0)           ### Names a variable, but does not create it in
 the backend
 x_0
 sage: mip.number_of_variables()
 0
 sage: mip[0]                  ### This now creates a variable. It prints
 the same as the result of gen(0), but is different.
 x_0
 sage: mip.get_values(mip.gen(0))
 [...]
 TypeError: Not a MIPVariable: x_0
 sage: mip.is_real(mip.gen(0))
 [...]
 KeyError: x_0
 sage: mip.is_real(mip[0])
 True
 }}}

--
Ticket URL: <http://trac.sagemath.org/ticket/20461#comment:6>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica, 
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