title: Why is Microsoft Solver Foundation not returning a solution?
body: <p>I'm trying to solve my linear program with Microsoft Solver Foundation, but it doesn't return a solution. It doesn't give a clear message to what is wrong, so I'm not sure what is going on. I have checked the constraints and I believe they are coded correctly, but maybe the LP model is wrong on itself? I would be glad if you can take a look at it and see what's wrong :)</p>
  <pre><code>===Solver Foundation Service Report===
  Date: 15/10/2021 16:00:21
  Version: Microsoft Solver Foundation 3.0.2.10889 Express Edition
  Model Name: DefaultModel
  Capabilities Applied: MILP
  Solve Time (ms): 51
  Total Time (ms): 103
  Solve Completion Status: Unknown
  Solver Selected: Microsoft.SolverFoundation.Solvers.SimplexSolver
  Directives:
  Simplex(TimeLimit = -1, MaximumGoalCount = -1, Arithmetic = Default, Pricing = Default, IterationLimit = -1, Algorithm = Default, Basis = Default, GetSensitivity = False)
  Algorithm: Primal
  Arithmetic: Exact
  Variables: 133 -&gt; 133 + 40
  Rows: 40 -&gt; 40
  Nonzeros: 522
  Eliminated Slack Variables: 0
  Basis: Slack
  Pivot Count: 0
  Phase 1 Pivots: 0 + 0
  Phase 2 Pivots: 0 + 0
  Factorings: 0 + 0
  Degenerate Pivots: 0 (0,00 %)
  Branches: 0
  </code></pre>
  <p>I'm making this for a practical assignment, so I prefer not to share my code. For information about the assignment: it's a machine assignment problem, where you have to plan two appointments for all patients. There are global parameters:</p>
  <ul>
  <li><strong>p1</strong>: the duration of the first appointment</li>
  <li><strong>p2</strong>: the duration of the second appointment</li>
  <li><strong>g</strong>: the gap between the first and second appointment</li>
  </ul>
  <p>Each patient needs two appointments <strong>t1</strong> and <strong>t2</strong> that need to be planned. Each patient also has personal parameters:</p>
  <ul>
  <li>interval <strong>I1=[r1, d1]</strong>, the time interval in which the first appointment can be planned</li>
  <li><strong>x</strong>: (personal) extra gap between the first and second appointment</li>
  <li>length <strong>l</strong>, the length of the second time interval. <strong>I2=[t1 + p1 + g + x, t1 + p1 + g + x + l - 1]</strong></li>
  </ul>
  <p><img src="https://i.stack.imgur.com/8pO97.png" alt="LP model1" /></p>