MATLAB Nexsys Model Function Definition

After the model definition line, the model file contains the definition of the function that implements the model code.

The second line in the model file must be the MATLAB function declaration line. The format of the function declaration line depends on the model type. Nexsys supports modeling of sources or input/output (I/O) model types, defined by the numbers of inputs and outputs.

A SOURCE model has no input ports (In_N =0) and one or more output ports (Out_N >0). A SOURC E model must have parameters NSAMP and SAMPLE_RATE in the parameter_list in the model definition line.

An I/O model has one or more input ports (In_N >0) and one or more output ports (Out_N >0). The format for the function declaration of an I/O model depends on whether or not it has a parameter_list in the model definition line.

For SOURCE UDMs the syntax for the function declaration line is:

function[outputs,SV] = function_name(parameters, SV, status_in)

For I/O UDMS with no parameter_list in the model definition line:

function[outputs,SV] = function_name(inputs, SV, status_in)

For I/O UDMS (In_N > 0) with a non-empty parameter_list in the model definition line:

function[outputs,SV] = function_name(inputs, parameters, SV, status_in)

The entries in the function declarations are defined as follows:

• outputs is the user-defined name of a two dimensional array with Out_N rows, each row corresponding to an output port in the same order specified in the UDM definition.
• inputs is a the user-defined name of a two dimensional array with In_N rows, each row corresponding to an input port in the same order specified in the UDM definition.
• parameters is the user-defined name of a one dimensional array containing the parameter values entered for the model instance in the same order defined in parameter_string.
• SV is a system-defined structure that retains the state variables of a MATLAB UDM. State variables are any structured data defined by the model file that must be saved between calls to the model. The first time a model is called, the simulator assigns a zero value to SV before passing it to the user-defined MATLAB function. During initialization (status_in = 0), the model saves any needed data structures in SV before passing the SV data back to Nexsys with the output of the function. Nexsys retains the SV information and passes it back to the MATLAB UDM function on the next invocation. If data retention is not required, the function does not need to initialize or set SV.
• status_in is a system-defined flag to indicate the input status when calling a MATLAB UDM function. (status_in = 0 for the initialization stage, nonzero otherwise.