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88 CHAPTER 3. FUNCTIONAL DESCRIPTION OF Xµ
and intstep are the interpolation order and integration step size. The system must be
continuous. The integration order and sample time are prespecified for discrete time
systems making the * operator is suitable for such simulations.
Xµ provides a sampled data simulation function (sdtrsp) based on the interconnection
structure shown in Figure 3.1.
Figure 3.1: Interconnection structure for sampled data simulation
The signals v and y are the continuous outputs of the continuous system, M(s). The
simulation assumes that y is sampled and used as the input to the discrete system,
N(z). The output of N(z), u(s) is assumed to be held with a zero order hold. All signals
are calculated with the sample spacing determined by the continuous time system
integration step size. The output of N(z) can be delayed by a fraction of the discrete
time system sample time. This is useful for simulating systems with a partial period
calculation delay; a situation which frequently occurs in practice.
3.4.3 Frequency Responses
The Xmath function freq is used for frequency response calculation. The input is a
Dynamic System and a vector of frequency points. The frequency points can
alternatively be specified by minimum and maximum variables and one of two other
choices: the total number of points or phase tracking. If the total number of points is
specified these are logarithmically spaced. If phase tracking is specified the points are
selected such that the phase difference between points is less than a prespecified