when I use the command **-run:test_cycles** it extremely increases the speed of modelling,
Please let me know why it does happen.Can I employ it?
-test_cycles is for testing Rosetta. It will run only a small number of cycles - these are not exact numbers, but it will run say 10 Monte Carlo cycles instead of 10,000. You cannot and should not use test_cycles for anything other than testing that Rosetta is compiled and working - certainly never for modeling.
It's the equivalent of baking a cake for 30 seconds instead of 30 minutes - you can see that the oven gets hot, but you aren't going to make a cake.