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Troubleshooting "No Feasible Solution" Errors in Solver

This article explains what "Solver could not find a feasible solution" means and gives the concrete steps you can take to address constraint-related issues in your model.

Summary

  • When Solver reports it cannot find a feasible solution, the model’s constraints and objective cannot be satisfied simultaneously.
  • Practical actions: inspect constraints for conflicts and adjust constraints as needed; one suggested action is to add constraints or modify existing ones.

What "no feasible solution" means

  • The constraints and the objective cannot be satisfied at the same time. In other words, there is no set of variable values that meets every constraint while also respecting the objective’s requirements.

Actions to take when you see a feasibility error

  1. Check for conflicting constraints

    • Review each constraint to confirm they do not contradict one another.
    • Ensure the mathematical relationships and bounds you set do not make it impossible for any solution to exist.

  2. Adjust or add constraints

    • Consider modifying constraint definitions or bounds so they are compatible with each other.
    • One option is to add constraints to the model where appropriate. (If you add constraints, verify they remain consistent with existing ones.)

Step-by-step approach

  1. Identify the infeasibility message from Solver.
  2. List all constraints and their bounds or formulas.
  3. Inspect constraints pairwise (or in logical groups) to detect contradictions (for example, mutually exclusive bounds).
  4. Decide whether to:
    • Relax a bound or remove/modify a constraint that is too restrictive, or
    • Add constraints that clarify model requirements or correct missing relationships.
  5. Re-run Solver after each change to confirm whether a feasible solution is found.

Troubleshooting tips

  • When changing constraints, make one change at a time and re-run Solver so you can identify which change resolves the issue.
  • If you suspect constraints conflict, focus on constraints that restrict the same variables or resources.

Conclusion A feasibility failure indicates the model’s constraints and objective cannot be satisfied together. Resolve this by checking for and removing conflicts among constraints, and by adjusting or adding constraints as needed to produce a compatible set of requirements.