Welcome to Adams/Solver Subroutines - Kxcad.net

Welcome to Adams/Solver Subroutines
You can call utility subroutines, such as AKISPL, CUBSPL, SYSARY, and SYSFNC, from VARSUB,
to obtain information about system variables, user-defined variables, and splines (see AKISPL,
CUBSPL, SYSARY, and SYSFNC).
The SYSARY and SYSFNC utility subroutines automatically set functional dependencies when the
VARSUB argument iflag is true. To compute solutions efficiently, Adams/Solver must know the other
variables on which each user-defined variable depends. Adams/Solver determines these functional
dependencies at the beginning of the simulation by calling VARSUB with the argument iflag set to true.
Adams/Solver does this once for each VARIABLE statement with a FUNCTION=USER() argument.
During each call to VARSUB, Adams/Solver records which calls you make to SYSARY and SYSFNC.
Adams/Solver assumes the user-defined variable depends on those system and user-defined variables,
and no others.
Tip: If the SYSARY or SYSFNC utility subroutines are called to access angular displacements,
the values returned by them may contain discontinuities. To avoid the discontinuities, use
the RCNVRT utility subroutine to convert the rotational angles from Euler angles to some
other rotational representation that does not encounter a singularity.
Caution: • When the iflag argument is true, you should make the same calls to SYSARY and
SYSFNC as you do to compute the value of the user-defined VARIABLE
statement. This ensures that Adams/Solver has the proper functional dependencies.
In general, Adams/Solver may have difficulty converging to a solution and/or may
take small integration steps if you fail to account for dependencies of the userdefined
VARIABLE statement. These results usually cause large increases in
execution time.
• When the iflag argument is true, SYSARY and SYSFNC return zero values for
system and user-defined variables. Computations that divide these values result in
system errors when you execute Adams/Solver. You should check for nonzero
values or ensure that the iflag argument is set to false before dividing by these
values.
• You must be careful when defining a VARIABLE statement dependent on another
VARIABLE statement, or on other Adams/Solver statements that contain
functions. If you define a system of equations without a stable solution, the
convergence may fail for the entire Adams/Solver model. The following example
refers to this type of VARIABLE statement:
VARIABLE/1,FUNCTION=VARVAL(1)+1
When looked at as an algebraic equation, it looks like the following:
V=V+1
However, when Adams/Solver tries to solve this equation using the Newton-Raphson
iteration, the solution diverges and a message indicates that the corrector has failed to
converge.
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