DSP Blockset

Zero Algorithmic Delay and Algebraic Loops.   When several blocks with zero algorithmic delay are connected in a feedback loop, Simulink may report an algebraic loop error and performance may generally suffer. You can prevent algebraic loops by injecting at least one sample of delay into a feedback loop (for example, by including an Integer Delay block with Delay > 0). See the Simulink documentation for more information about algebraic loops.

Zero Algorithmic Delay

Basic Algorithmic Delay