Learn more about Simulink

mdlDerivatives - Compute the S-function's derivatives

Required

C Syntax

#define MDL_DERIVATIVES

void mdlDerivatives(SimStruct *S)

C Arguments

S: SimStruct representing an S-Function block.

M Syntax

Derivatives(s)

M Arguments

s: Instance of Simulink.MSFcnRunTimeBlock class representing the Level-2 M-File S-Function block

Description

The Simulink engine invokes this optional method at each time step to compute the derivatives of the S-function's continuous states. This method should store the derivatives in the S-function's state derivatives vector. In a C MEX S-function, use ssGetdX to get a pointer to the derivatives vector. In a Level-2 M-file S-function, use the run-time object's Derivatives method.

Each time the mdlDerivatives routine is called, it must explicitly set the values of all derivatives. The derivative vector does not maintain the values from the last call to this routine. The memory allocated to the derivative vector changes during execution.

Note When generating code for a noninlined C MEX S-function that contains this method, make sure the method is not wrapped in a #if defined(MATLAB_MEX_FILE) statement. For example:

#define MDL_DERIVATIVES 
#if defined(MDL_DERIVATIVES) && defined(MATLAB_MEX_FILE) 
static void mdlDerivatives(SimStruct *S) 
{ 
   /* Add mdlDerivatives code here *
} 
#endif

The define statement makes the mdlDerivatives method available only to a MATLAB MEX-file. If the S-function is not inlined, the Real-Time Workshop product cannot use this method, resulting in link or run-time errors.

C Example

For a C MEX S-function example, see matlabroot/toolbox/simulink/simdemos/simfeatures/src/csfunc.c.

M Example

For a Level-2 M-file S-function example, see matlabroot/toolbox/simulink/simdemos/simfeatures/ msfcn_limintm.m.

Languages

C, C++, M