For gases the conservative variables , and are smoothed on basis of the local pressure gradient which was calculated in the previous fluid increment (subroutine presgradient.f). The smoothing is done in routine smoothshock.f. The primary parameter in the smoothing procedure is shockcoef, which can take values between 0 (no smoothing) and 2. This parameter can be set in the input deck on the *STEP card using the parameter SHOCK SMOOTHING. If the solution diverges (this is frequently characterized by the presence of NaN (Not a Number) in the solution, leading to negative time steps or the divergence of the conservative to physical conversion routine con2phys.f), the calculation if restarted with a shock smoothing coefficient twice the previous value (or a value of 0.001 if the previous value was 0). Once the value of 2 is exceeded, the program stops with an error message.