7.2 Errors and exceptionsΒΆ

Exceptions

Almost every function in Optimizer API for Python can throw an exception informing that the requested operation was not performed correctly, and indicating the type of error that occurred. This is the case in situations such as for instance:

  • referencing a nonexisting variable (for example with too large index),
  • defining an invalid value for a parameter,
  • accessing an undefined solution,
  • repeating a variable name, etc.

It is therefore a good idea to catch exceptions of type Error. The one case where it is extremely important to do so is when Task.optimize is invoked. We will say more about this in Section 7.1.

The exception contains a response code (element of the enum rescode) and short diagnostic messages. They can be accessed as in the following example.

try:
  task.putdouparam(mosek.dparam.intpnt_co_tol_rel_gap, -1.0e-7)
except mosek.Error as e: 
  print("Response code {0}\nMessage       {1}".format(e.errno, e.msg))

It will produce as output:

Response code rescode.err_param_is_too_small
Message       The parameter value -1e-07 is too small for parameter 'MSK_DPAR_INTPNT_CO_TOL_REL_GAP'.

Another way to obtain a human-readable string corresponding to a response code is the method Env.getcodedesc. A full list of exceptions, as well as response codes, can be found in the API reference.

Optimizer errors and warnings

The optimizer may also produce warning messages. They indicate non-critical but important events, that will not prevent solver execution, but may be an indication that something in the optimization problem might be improved. Warning messages are normally printed to a log stream (see Section 7.3). A typical warning is, for example:

MOSEK warning 53: A numerically large upper bound value  6.6e+09 is specified for constraint 'C69200' (46020).

Warnings can also be suppressed by setting the iparam.max_num_warnings parameter to zero, if they are well-understood.