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234 GNU OctavesysrepdemoTutorial for the use of the system data structure functions.Function File29.1.1 Variables common to all ocst system formatsThe data structure elements (and variable types) common to all system representationsare listed below; examples of the initialization and use of the system data structures aregiven in subsequent sections and in the online demo DEMOcontrol.nnzinnameoutnamesysThe respective number of continuous and discrete states in the system (scalar)list of name(s) of the system input, output signal(s). (list of strings)System status vector. (vector)This vector indicates both what representation was used to initialize the systemdata structure (called the primary system type) and which other representationsare currently up-to-date with the primary system type (see Section 29.2.5[structaccess], page 241).The value of the first element of the vector indicates the primary system type.0 for tf form (initialized with tf2sys or fir2sys)1 for zp form (initialized with zp2sys)2 for ss form (initialized with ss2sys)The next three elements are boolean flags that indicate whether tf, zp, or ss,respectively, are “up to date" (whether it is safe to use the variables associatedwith these representations). These flags are changed when calls are made tothe sysupdate command.tsamydDiscrete time sampling period (nonnegative scalar). tsam is set to 0 for continuoustime systems.Discrete-time output list (vector)indicates which outputs are discrete time (i.e., produced by D/A converters)and which are continuous time. yd(ii) = 0 if output ii is continuous, = 1 ifdiscrete.The remaining variables of the system data structure are only present if the correspondingentry of the sys vector is true (=1).29.1.2 tf format variablesnumdennumerator coefficients (vector)denominator coefficients (vector)