Here the solution I found :

```
private static IEnumerable<int> ComputeMatrix(int[,] matrix)
{
// check args
if (matrix.Rank != 2) { throw new ArgumentException("matrix should have a rank of 2"); }
if (matrix.GetUpperBound(0) != matrix.GetUpperBound(1)) { throw new ArgumentException("matrix should have the same size");}
// indice treated
List<int> treatedIndex = new List<int>();
for (int i = 0; i <= matrix.GetUpperBound(0); i++)
{
if (treatedIndex.Count == matrix.GetUpperBound(0))
break;
// distance minimum between 2 points
int distanceMin = Int32.MaxValue;
// next iteration of index
int nextI = i;
// add the index to ignore in the next iteration
int nextJ = -1;
for (int j = 0; j <= matrix.GetUpperBound(1); j++)
{
if (treatedIndex.IndexOf(j) == -1)
{
if (matrix[i, j] != 0 && matrix[i, j] < distanceMin)
{
distanceMin = matrix[i, j];
nextI = j;
nextJ = i;
}
}
}
i = nextI - 1;
treatedIndex.Add(nextJ);
yield return distanceMin;
}
}
```

solved Browse a matrix