[Scip] Can I tell SCIP to refrain from fixing/aggregating some variables?

[Daniel Karch]

Hi everyone,

I have the following problem. In my model I have continuous variables x0 andy
, binary variables x1, ..., xk, and linear constraints of the following
form:

1)         x1 +    x2 + ... +    xk = 1
2) x0 + a1*x1 + a2*x2 + ... + ak*xk = y
3) lb <= x0 <= ub

There are other constraints, too, but they do not matter here.
The objective is to minimize y.
The idea is that I can write y as

y = ai + x0,

for some i so that I can branch on the variables xi during the algorithm.
But I don't know the coefficients ai and the bounds lb and ub beforehand,
and the constraints 2) and 3) are added later on, once I have determined
the missing pieces.
Now SCIP does not know that x0 will become important later on and fixes it
to zero.
Is there a way to exclude the variables xi from the presolving or to
explicitly forbid fixing or aggregating them?

Best regards,

  Daniel
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