# 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 

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