[SCIP] Help With Infeasibility and Constraint Issues in SCIP Implementation

[Mahdi Mohammadi]

Dear SCIP Development Team,

First, I would like to express my gratitude for providing such a powerful
and freely accessible framework to the scientific community. Your work has
significantly advanced research in optimization and related fields.

I am reaching out regarding an issue I have been struggling with while
implementing my model in SCIP. My implementation is based on the
bin-packing problem example you provided in C language. However, I am
encountering difficulties with one of my pricing constraints.
Specifically, when I use the following linear constraint:

SCIPcreateConsBasicLinear(subscip, &cons, "sum_cap", nvars, vars, vals,
capacity, capacity);

The problem becomes infeasible. I am unsure how to debug and identify the
source of the infeasibility, as I have not found a way to generate detailed
diagnostic reports similar to those in GAMS, CLPEX and etc.
Meanwhile, when I replace the linear constraint with a knapsack inequality
as shown below, the instances become feasible but yield incorrect solutions
for some cases:

SCIPcreateConsBasicKnapsack(subscip, &cons, "sum_cap", nvars, vars, vals,
capacity);

Interestingly, when I set the left-hand side of the linear constraint to
zero, the problem becomes feasible again but produces another incorrect
feasible solution. Since the problem's objective is maximizing this should
not happen.

To summarize, I would greatly appreciate your guidance on the following:

1. How can I debug infeasibility in SCIP similar to GAMS to identify the
root cause? I want to see the result of summation in the constraint that is
infeasible.
2. Could this issue be related to numerical precision? For example, I have
an instance that is solved correctly with the knapsack constraint but
becomes infeasible when replaced with the linear constraint while
everything is OK.
For reference, I have attached the relevant model definitions.

Thank you for your time and assistance. I look forward to hearing your
advice on how to resolve this issue.

Best regards,
Mahdi Mohammadi
------------------------------------------------
PS:
I sent this email some minutes ago, but back then my email hasn't been
aproved by moderater and I've just recieved the email. I'm sorry if it is
duplicated.
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