Creating and Manipulating Models

Chapter 3
Model Analysis Tools

General Model Characteristics

General model characteristics include the model type, I/O dimensions, and continuous or discrete nature. Related commands are listed in the table below. These commands operate on continuous- or discrete-time LTI models or arrays of LTI models of any type.

General Model Characteristics Commands
class	Display model type ('tf', 'zpk', 'ss', or 'frd').
hasdelay	Test true if LTI model has any type of delay.
isa	Test true if LTI model is of specified class.
isct	Test true for continuous-time models.
isdt	Test true for discrete-time models.
isempty	Test true for empty LTI models.
isproper	Test true for proper LTI models.
issiso	Test true for SISO models.
ndims	Display the number of model/array dimensions.
reshape	Change the shape of an LTI array.
size	Output/input/array dimensions. Used with special syntax, size also returns the number of state dimensions for state-space models, and the number of frequencies in an FRD model.

This example illustrates the use of some of these commands. See the related reference pages for more details.

H = tf({1 [1 -1]},{[1 0.1] [1 2 10]})

Transfer function from input 1 to output:
   1
-------
s + 0.1
 
Transfer function from input 2 to output:
    s - 1
--------------
s^2 + 2 s + 10

class(H)

ans =
tf

size(H)
Transfer function with 2 input(s) and 1 output(s).

[ny,nu] = size(H)% Note: ny = number of outputs

ny =
     1
 
nu =
     2

isct(H)% Is this system continuous?
 
ans =
     1

isdt(H)% Is this system discrete?
 
ans =
      0

References

Model Dynamics