The flag LOGDFL should be set

• .TRUE. if the Logd integrator is to be used
• .FALSE. if the Logd integrator is not to be used

If LOGDFL is .FALSE., then RENDLD is set equal to RSTART.

⚠️ Since the width of the first interval in the Airy propagation is equal to SPAC x FSTFAC, even if LOGDFL is set .FALSE., SPAC should be given a non-zero value.