User`s guide

Examples of C MEX-File S-Function Blocks
3-85
matlabroot/simulink/src/stvctf.c
/*
* File : stvctf.c
* Abstract:
* Time Varying Continuous Transfer Function block
*
* This S-function implements a continuous time transfer function
* whose transfer function polynomials are passed in via the input
* vector. This is useful for continuous time adaptive control
* applications.
*
* This S-function is also an example of how to "use banks" to avoid
* problems with computing derivatives when a continuous output has
* discontinuities. The consistency checker can be used to verify that
* your S-function is correct with respect to always maintaining smooth
* and consistent signals for the integrators. By consistent we mean that
* two mdlOutput calls at major time t and minor time t are always the
* same. The consistency checker is enabled on the diagnostics page of the
* simulation parameters dialog box. The update method of this S-function
* modifies the coefficients of the transfer function, which cause the
* output to "jump." To have the simulation work properly, we need to let
* the solver know of these discontinuities by setting
* ssSetSolverNeedsReset. Then we need to use multiple banks of
* coefficients so the coefficients used in the major time step output
* and the minor time step outputs are the same. In the simulation loop
* we have:
* Loop:
* o Output in major time step at time t
* o Update in major time step at time t
* o Integrate (minor time step):
* o Consistency check: recompute outputs at time t and compare
* with current outputs.
* o Derivatives at time t.
* o One or more Output,Derivative evaluations at time t+k
* where k <= step_size to be taken.
* o Compute state, x.
* o t = t + step_size.
* End_Integrate
* End_Loop
* Another purpose of the consistency checker is used to verify that when
* the solver needs to try a smaller step size that the recomputing of
* the output and derivatives at time t doesn't change. Step size
* reduction occurs when tolerances aren't met for the current step size.
* The ideal ordering would be to update after integrate. To achieve
* this we have two banks of coefficients. And the use of the new
* coefficients, which were computed in update, are delayed until after
* the integrate phase is complete.
*
* See simulink/src/sfuntmpl.doc.
*
* Copyright (c) 1990-1998 by The MathWorks, Inc. All Rights Reserved.
* $Revision: 1.8 $