# 6.2. Control Contact: Control Subset

    BEGIN CONTROL CONTACT
      CONTROL SUBSET = ADAGIO|ALL|ARS|JAS|SST
    END

By default all implicit contact constraints are enforced simultaneously. The `CONTROL SUBSET` option to the control contact solver block is an experimental option for enforcing different types of constraints at different levels of the multilevel solver. For example the following input will control the node face (ADAGIO) contact constraints at level one and the analytic rigid surface contact constraints (ARS) at level two. This means that ARS constraints are found held constant while ADAGIO constraints are iteratively solved. Then the ARS constraints are updated and again held constant while the ADAGIO constraints are iteratively solved again.

    begin control contact control_al
      level = 1
      target relative residual = 5.e-04
      control subset = ADAGIO
    end control contact

    begin control contact control_ars
      level = 2
      target relative residual = 1.e-3
      control subset = ARS
    end control contact

Use of the `CONTROL SUBSET` will substantially increase analysis cost, but may lead to more robust convergence if the model contains potentially conflicting contact constraint types acting on the same nodes.