# Engine

In /DT/AMS/Iflag if `I`_{flag}= 1, the tolerance for AMS convergence,
`Tol_AMS`, must be provided. If `I`_{flag} is ignored, the default value (1E-3) for
`Tol_AMS` is applied. It is not recommended to modify AMS
tolerance, if it is not needed. Note that `Tol_AMS` was 1E-4 in
12.0.210.

`I`

_{flag}= 2, the display of the number of AMS iterations may help in debugging or monitoring convergence at no extra CPU cost. Maximum allowed iterations before sending a divergence message is 1000 by default. It is advised to NOT change this value. Anything above this maximum value, Radioss stops with the following error message:

** ERROR ** AMS IS LIKELY DIVERGING

- Monitoring the number of iterations per cycle can help to understand the
resulting AMS performance:
75 to 100 iterations is a sign of a really bad convergence 50 iterations may not provide any speedup 30 iterations or less is considered a good convergence.

It is advised to use 0.67 as the scale factor, $\text{\Delta}{T}_{sca}$ , rather than 0.9 (as well as in traditional nodal mass scaling /DT/NODA/CST, especially if it is used for comparison with the AMS results).

Target a minimum time step, $\text{\Delta}{T}_{\mathrm{min}}$ , from 10 to 20 times than the one used in /DT/NODA/CST, that is, start with 10 times, then check how far to go by verifying the numerical convergence, the gain of elapsed time, and the results quality.

- The global momentum of the related nodes is conserved.
- A comparison with traditional mass scaling requires a minor added mass along the /DT/NODA/CST computation, if used as a reference.

/DT/Eltyp/Keyword3 is compatible with /DT/AMS, except /DT/INTER/CST (refer to Capabilities and Limitations for further details).

Use /DT/INTER/DEL as a workaround for slow convergence, or possible divergence, when invoking a nonlinear penalty stiffness with contact interfaces TYPE7, TYPE11, and TYPE19.

/ANIM/NODA/NDMAS may be added in order to output non-diagonal mass variation.

/ANIM/NODA/DINER may be added in order to output added inertia per nodes.