```json
{
  "sym_variables": [
    ("x0", "grams of fiber"),
    ("x1", "milligrams of vitamin E")
  ],
  "objective_function": "3.18 * x0 + 3.26 * x1",
  "constraints": [
    "10 * x0 + 11 * x1 >= 13",
    "13 * x0 + 12 * x1 >= 18",
    "16 * x0 + 10 * x1 >= 16",
    "5 * x0 - 10 * x1 >= 0",
    "10 * x0 + 11 * x1 <= 61",
    "13 * x0 + 12 * x1 <= 50",
    "16 * x0 + 10 * x1 <= 46"
  ]
}
```

The problem is infeasible.  The constraints 5x0 - 10x1 >= 0 and 16x0 + 10x1 <= 46 imply that x0 <= 2.  However, 13x0 + 12x1 <= 50 and 13x0 + 12x1 >= 18, together with x0 <=2, imply that 26 + 12x1 <= 50 and 26 + 12x1 >= 18. This means 2 <= x1 <= 2, so x1 = 2.  But then 16x0 + 10x1 <= 46 becomes 16x0 + 20 <= 46, so 16x0 <= 26, which means x0 <= 1.625. Since x0 must be an integer, x0 <= 1.  However, if x0 = 1 and x1 = 2, then 5x0 - 10x1 = 5 - 20 = -15, which violates the constraint 5x0 - 10x1 >= 0.  If x0 = 0, then 5x0 - 10x1 >= 0 implies x1 <= 0, but 10x0 + 11x1 >= 13 becomes 11x1 >= 13, so x1 >= 13/11 > 0.  Thus, there are no feasible solutions.

```python
import gurobipy as gp

try:
    # Create a new model
    m = gp.Model("optimization_problem")

    # Create variables
    x0 = m.addVar(vtype=gp.GRB.INTEGER, name="grams_of_fiber")
    x1 = m.addVar(vtype=gp.GRB.CONTINUOUS, name="milligrams_of_vitamin_E")

    # Set objective function
    m.setObjective(3.18 * x0 + 3.26 * x1, gp.GRB.MAXIMIZE)

    # Add constraints
    m.addConstr(10 * x0 + 11 * x1 >= 13, "c0")
    m.addConstr(13 * x0 + 12 * x1 >= 18, "c1")
    m.addConstr(16 * x0 + 10 * x1 >= 16, "c2")
    m.addConstr(5 * x0 - 10 * x1 >= 0, "c3")
    m.addConstr(10 * x0 + 11 * x1 <= 61, "c4")
    m.addConstr(13 * x0 + 12 * x1 <= 50, "c5")
    m.addConstr(16 * x0 + 10 * x1 <= 46, "c6")


    # Optimize model
    m.optimize()

    if m.status == gp.GRB.OPTIMAL:
        print('Obj: %g' % m.objVal)
        print('x0: %g' % x0.x)
        print('x1: %g' % x1.x)
    elif m.status == gp.GRB.INFEASIBLE:
        print('The problem is infeasible.')
    else:
        print('Optimization ended with status %d' % m.status)


except gp.GurobiError as e:
    print('Error code ' + str(e.errno) + ': ' + str(e))

except AttributeError:
    print('Encountered an attribute error')
```