```json
{
  "sym_variables": [
    ("x0", "milligrams of vitamin D"),
    ("x1", "milligrams of calcium"),
    ("x2", "milligrams of vitamin B2")
  ],
  "objective_function": "6.46 * x0 + 1.98 * x1 + 6.73 * x2",
  "constraints": [
    "23 * x0 + 33 * x2 >= 28",
    "23 * x0 + 34 * x1 >= 51",
    "23 * x0 + 34 * x1 + 33 * x2 >= 51",
    "10 * x0 + 9 * x2 >= 23",
    "10 * x0 + 11 * x1 >= 20",
    "11 * x1 + 9 * x2 >= 40",
    "10 * x0 + 11 * x1 + 9 * x2 >= 46",
    "10 * x0 + 11 * x1 + 9 * x2 >= 46",  // Redundant constraint
    "23 * x0 + 33 * x2 <= 168",
    "x0 >= 0",
    "x1 >= 0",
    "x2 >= 0"
  ]
}
```

```python
import gurobipy as gp

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

    # Create variables
    vitamin_d = m.addVar(lb=0, vtype=gp.GRB.CONTINUOUS, name="vitamin_d")
    calcium = m.addVar(lb=0, vtype=gp.GRB.CONTINUOUS, name="calcium")
    vitamin_b2 = m.addVar(lb=0, vtype=gp.GRB.CONTINUOUS, name="vitamin_b2")


    # Set objective function
    m.setObjective(6.46 * vitamin_d + 1.98 * calcium + 6.73 * vitamin_b2, gp.GRB.MINIMIZE)

    # Add constraints
    m.addConstr(23 * vitamin_d + 33 * vitamin_b2 >= 28, "c1")
    m.addConstr(23 * vitamin_d + 34 * calcium >= 51, "c2")
    m.addConstr(23 * vitamin_d + 34 * calcium + 33 * vitamin_b2 >= 51, "c3")
    m.addConstr(10 * vitamin_d + 9 * vitamin_b2 >= 23, "c4")
    m.addConstr(10 * vitamin_d + 11 * calcium >= 20, "c5")
    m.addConstr(11 * calcium + 9 * vitamin_b2 >= 40, "c6")
    m.addConstr(10 * vitamin_d + 11 * calcium + 9 * vitamin_b2 >= 46, "c7")
    m.addConstr(23 * vitamin_d + 33 * vitamin_b2 <= 168, "c8")


    # Optimize model
    m.optimize()

    # Print results
    if m.status == gp.GRB.OPTIMAL:
        print('Obj: %g' % m.objVal)
        print('vitamin_d:', vitamin_d.x)
        print('calcium:', calcium.x)
        print('vitamin_b2:', vitamin_b2.x)
    elif m.status == gp.GRB.INFEASIBLE:
        print('Optimization 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')
```