# Retrieve Solver Log Files in AIMMS Developer¶

Solvers can share information about the solution process up to a very detailed level. To avoid overhead in generating information that is not inspected anyway, the AIMMS IDE defaults to not sharing any information.

## Get started with log files¶

The first option is to set the option `solver_listing_messages`

to `all`

.
By just setting this option, a solver will generate a small log file with the name `<solver name>.sta`

in the folder `log`

.
The first solve of an AIMMS session will create the file, subsequent solves will append to the file.
To generate a log file, I used the Flow Shop problem with 14 jobs and 20 machines and solved it using CPLEX 12.8 on my desktop.

1 2 3 4 5 6 | ```
Solve problem 'FlowShopModel' with 554 rows, 476 columns (196 binaries, 0 generals), and 8808 nonzeros.
MIP - Integer optimal solution: Objective = 3.8900000000e+002
Solution time = 71.72 sec. Iterations = 6163443 Nodes = 101990
``` |

## Additional information and example¶

For a MIP problem, a typical first setting to add is the option `MIP display`

to `Display each nth node`

.
Thus I obtained a 95 line log file `log\cplex 12.8.sta`

.
For the sake of brevity, I only show the first and last five lines here.

1 2 3 4 5 | ```
Solve problem 'FlowShopModel' with 554 rows, 476 columns (196 binaries, 0 generals), and 8808 nonzeros.
Tried aggregator 3 times.
MIP Presolve eliminated 0 rows and 1 columns.
MIP Presolve modified 7561 coefficients.
Aggregator did 25 substitutions.
``` |

Last five lines:

90 91 92 93 94 | ```
------------
Total (root+branch&cut) = 72.72 sec. (45534.38 ticks)
MIP - Integer optimal solution: Objective = 3.8900000000e+002
Solution time = 72.72 sec. Iterations = 6163443 Nodes = 101990
``` |

## Overview of options to try out first for logging¶

This section presents, based on problem type and solver, a list of first options to be set for more information. This is not a list of options to improve performance, but a first step to obtain more information about the solution process so analysis of the solution process can be started.

### LP Problems solved using Barrier¶

Solver | Option | Value |
---|---|---|

CPLEX | Barrier display | Normal |

GUROBI | Output file | yes |

CBC | Status File | File |

### LP Problems solved using SIMPLEX¶

Solver | Option | Value |
---|---|---|

CPLEX | Simplex display | At refactorizations |

GUROBI | Output file | yes |

CBC | Status File | File |

### MIP Problems¶

Solver | Option | Value |
---|---|---|

CPLEX | MIP display | Display each nth node |

GUROBI | Output file | yes |

CBC | Status File | File |

### NLP Problems¶

Solver | Option | Value |
---|---|---|

BARON | Keep results file | On |

CONOPT | Status file display | Iteration log |

IPOPT | Status file | Yes |

KNITRO | Status file display | Summary |

SNOPT | Print output file | On |