Catalog of Model Interconnections

Each type of block diagram connection corresponds to a model interconnection command or arithmetic expression. The following tables summarize the block diagram connections with the corresponding interconnection command and arithmetic expression.

Model Interconnection Commands

Block Diagram Connection	Command	Arithmetic Expression
	series(H1,H2)	H2*H1
	parallel(H1,H2)	H1+H2
	parallel(H1,-H2)	H1-H2
	feedback(H1,H2)	H1/(1+H2*H1) (not recommended)
	N/A	H1/H2 (division)
	N/A	H1\H2 (left division)
	inv(H1)	N/A
	lft(H1,H2,nu,ny)	N/A

Arithmetic Operations

You can apply almost all arithmetic operations to dynamic system models, including those shown below.

Operation	Description
+	Addition
-	Subtraction
*	Multiplication
.*	Element-by-element multiplication
/	Right matrix divide
\	Left matrix divide
inv	Matrix inversion
'	Conjugate transposition. See ctranspose.
.'	Transposition
^	Powers of a dynamic system model, as in the following syntax for creating transfer functions: s = tf('s'); G = 25/(s^2 + 10*s + 25);

In some cases, you might obtain better results using model interconnection commands, such as feedback or connect, instead of model arithmetic. For example, the command T = feedback(H1,H2) returns better results than the algebraic expression T = H1/(1+H2*H1). The latter expression duplicates the poles of H1, which inflates the model order and might lead to computational inaccuracy.