User`s guide

Examples of C MEX-File S-Function Blocks
3-79
* and having a continuous sample time. Solvers work best on smooth problems.
* In order for the solver to work without chattering, limit cycles, or
* similar problems, it is absolutely crucial that the same equation be used
* throughout the duration of a MajorTimeStep. To visualize this, consider
* the case of the Saturation block feeding an Integrator block.
*
* To implement this rule, the mode vector is used to specify the
* valid equation based on the following:
*
* if UpperLimit < u then use (1)
* if LowerLimit <= u <= UpperLimit then use (2)
* if u < LowerLimit then use (3)
*
* The mode vector is changed only at the beginning of a MajorTimeStep.
*
* During a minor time step, the equation specified by the mode vector
* is used without question. Most of the time, the value of u will agree
* with the equation specified by the mode vector. However, sometimes u's
* value will indicate a different equation. Nonetheless, the equation
* specified by the mode vector must be used.
*
* When the mode and u indicate different equations, the corresponding
* calculations are not correct. However, this is not a problem. From
* the ZC function, the solver will know that an equation switch occurred
* in the middle of the last MajorTimeStep. The calculations for that
* time step will be discarded. The ZC function will help the solver
* find the exact instant at which the switch occurred. Using this knowledge,
* the length of the MajorTimeStep will be reduced so that only one equation
* is valid throughout the entire time step.
*/
static void mdlOutputs(SimStruct *S, int_T tid)
{
InputRealPtrsType uPtrs = ssGetInputPortRealSignalPtrs(S,0);
real_T *y = ssGetOutputPortRealSignal(S,0);
int_T numOutput = ssGetOutputPortWidth(S,0);
int_T iOutput;
/*
* Set index and increment for input signal, upper limit, and lower limit
* parameters so that each gives scalar expansion if needed.
*/
int_T uIdx = 0;
int_T uInc = ( ssGetInputPortWidth(S,0) > 1 );
real_T *upperLimit = mxGetPr( P_PAR_UPPER_LIMIT );
int_T upperLimitInc = ( mxGetNumberOfElements( P_PAR_UPPER_LIMIT ) > 1 );
real_T *lowerLimit = mxGetPr( P_PAR_LOWER_LIMIT );
int_T lowerLimitInc = ( mxGetNumberOfElements( P_PAR_LOWER_LIMIT ) > 1 );
if (ssGetNumNonsampledZCs(S) == 0) {
/*
* This block is being used with a fixed-step solver or it has
* a noncontinuous sample time, so we always saturate.
*/