Welcome to Adams/Solver Subroutines - Kxcad.net

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Adams/Solver
Note that the computational savings are not always so generous. Consider a function F that
depends on the two 6D measures, DISP and VEL, of a single PART marker, with respect to
ground. During finite differencing, F must be evaluated 12 times, once for each dimension of
each measure. Meanwhile, the function only depends on the 12 generalized displacements and
velocities of the PART, so the
FORTRAN 77 Adams/Solver would also only have needed 12 evaluations of F.
• Because you are aware of the functional dependency of the function, F, on the measured
∂ F
---------
∂ Mj quantities, Mi, computing may be straightforward. Adams/Solver (C++) provides
SYSPAR: an interface you can use to register these partial derivatives, in the cases where they
are known and can be efficiently computed.
Note that the potential of user-provided partial derivatives does not only affect the computational
cost of evaluating the system Jacobian, but can also improve the accuracy of simulations and the
rate of convergence. This is because your analytical derivatives are likely to be more accurate
than those obtained using finite differencing. When Adams/Solver uses the Jacobian directly, as
in Adams/Linear, the quality of the solution may also be improved.
When F and M have dimension greater than 1, the partial matrix, should be stored in partl
in FORTRAN 77 style column order. In other words, all the partial derivatives of F with respect
to the first component of M come before the partial derivatives of F with respect to the second
component of M, and so on.
Each call to SYSFNC/SYSARY creates what the previous section refers to as a measure. For
each of these measures, the creator of the user subroutine is allowed to register the partials of the
function with respect to this measure.
You do not need partial derivatives during every call to the user's subroutine, because they are
only needed when the Jacobian is being evaluated. You must request the flag that indicates
whether the partial derivatives are required, by calling the following function:
CALL ADAMS_NEEDS_PARTIALS(PARFLG)
∂ F
---------
∂ Mj Note that, ideally, the PARFLG would have been added to the user subroutine call, alongside
IFLAG and DFLAG, but the user subroutines have a standard interface that cannot be changed.