Chapter 3 Building System Connections
© National Instruments Corporation 3-9 Xmath Control Design Module
• By default, feedback is defined to be positive. To enforce negative
feedback, specify connect(Sys,-K).
• A “selection matrix” has a single 1 in each row; the rest of the row
contains zeros. This is useful for indicating the subset of system inputs
and outputs to be used. In many cases, however, it is simpler to extract
desired inputs and outputs through indexing.
• Both systems must have the same sample rate.
• Improper dynamic systems—systems with more zeros than poles—are
not allowed.
The number of outputs in the combined system is the sum of the number of
outputs from the two systems you are appending. For an example of how to
use gains for the input, the output, and the fed-back data, refer to
Example 3-3.
Example 3-3 Using connect( ) to Perform a General Output-Input Connection
tfsys=system(makepoly([1,2]),makepoly([1,3,0]))
tfsys (a transfer function) =
x + 2
-------
2
x + 3x
initial integrator outputs
0
0
Input Names
-----------
Input 1
Output Names
------------
Output 1
System is continuous
connect(tfsys,0.12,2,1.5)
ans (a state space system) =
A
-3 1
-0.12 0.12
B
0