[SCIP] Get auxiliary variables from reformulated expression graph

[liding xu]

Dear SCIP community,
    I am aware that scip uses an expression graph to represent general
nonlinear functions and constructs its  linear under-estimators via
factorizable programming. Given a general nonlinear function (e.g.
signomial functions), scip adds auxiliary variables and constraints
associated with some intermediate nodes of the expression graph.
  I have the following common questions:
  1. In which phase (e.g. transformation, resolve), does scip reformulate
the expression graph to a set of auxiliary variables and constraints?
  2.How can get these auxiliary variables after reformulation, i.e.
(SCIP_VAR *) and constraints (SCIP_CONS*)?
  3. For example, given a signomial function f(x)  = \sum_i s_i(x), where
\sum_i s_i(x) =  c_i \prod_j x_j^{p_{ij}}.  how can I get the variable
associated to the signomial term s_i(x) = c_i \prod_j x_j^{p_{ij}}?

 Best wishes,
Liding Xu
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