def set_variable_type(index, type)
      case type
      when :continuous
        Cbc.Cbc_setContinuous @ptr, index
      when :integer, :binary
        Cbc.Cbc_setInteger @ptr, index
      else
        fail :type
      end
    end
def set_variable_type(index, type)
      case type
      when :continuous
        Cbc.Cbc_setContinuous @ptr, index
      when :integer, :binary
        Cbc.Cbc_setInteger @ptr, index
      else
        fail :type
      end
    end
Set the type of a variable