Creating and Manipulating Models

Automatic Conversion

Some algorithms operate only on one type of LTI model. For example, the algorithm for zero-order-hold discretization with c2d can only be performed on state-space models. Similarly, commands like tfdata expect one particular type of LTI models (TF). For convenience, such commands automatically convert LTI models to the appropriate or required model type. For example, in

• sys = ss(0,1,1,0)
  [num,den] = tfdata(sys)
  

tfdata first converts the state-space model sys to an equivalent transfer function in order to return numerator and denominator data.

Note that conversions to state-space models are not uniquely defined. For this reason, automatic conversions to state space are disabled when the result depends on the choice of state coordinates, for example, in commands like initial or kalman.

Explicit Conversion

Caution About Model Conversions