The number of nonzeros in the lower triangle of AAT gives an early indication of how long each barrier iteration will take in terms of a relative measure of time. The larger this number, the more time each barrier iteration requires. If this number is close to 50% of the square of the number of rows of the reduced LP, then the problem may contain dense columns that are not being detected. In that case, examine the histogram of column counts; then consider setting the barrier column-nonzeros parameter to a value that enables ILOG CPLEX to treat more columns as being dense.

In the Interactive Optimizer, you can examine the histogram of column counts with the command display problem histogram.