Cadyts (Calibration of dynamics traffic simulations) is a package developed by Gunnar Flötteröd, which takes measurements as input and provides corrections as output. Those corrections can be used as weights during plans choice, bringing the system closer to the measurement.

See here or search for "cadyts" on the web.

For examples see the org.matsim.contrib.cadyts.run package.

Packages 
Package Description
org.matsim.contrib.cadyts.car
Cadyts infrastructure for car plan calibration based on link traffic counts.
org.matsim.contrib.cadyts.general
Cadyts infrastructure that is shared between the car and the pt setup.
org.matsim.contrib.cadyts.measurement  
org.matsim.contrib.cadyts.pt
Integrates automatic calibration upon public transport line occupancies using Cadyts into MATSim.
org.matsim.contrib.cadyts.run
Contains "scripts-in-java" to run cadyts with matsim.
org.matsim.contrib.cadyts.utils