Polynomial Stability Test

R2026b

Use Schur-Cohn algorithm to determine whether all roots of input polynomial are inside unit circle

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Polynomial Stability Test block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
DSP System Toolbox / Math Functions / Polynomial Functions

Description

The Polynomial Stability Test block uses the Schur-Cohn algorithm to determine whether all roots of a polynomial are within the unit circle.

This is the equivalent MATLAB^® code for the block.

y = all(abs(roots(u)) < 1)

This block is most commonly used to check the pole locations of the denominator polynomial A(z) of a transfer function H(z).

$$H(z)=\frac{B(z)}{A(z)}=\frac{b_1+b_2{z}^{-1}+\dots +b_m{z}^{-(m-1)}}{a_1+a_2{z}^{-1}+\dots +a_n{z}^{-(n-1)}}$$

The poles are the n − 1 roots of the denominator polynomial A(z). When any poles are located outside the unit circle, the transfer function H(z) is unstable. As is typical in DSP applications, the transfer function H(z) is specified in descending powers of z⁻¹ rather than z.

Ports

Input

Input — Input polynomial

vector | matrix

Specify the input polynomial as a vector or a matrix of size M-by-N.

Each column of the input matrix u contains M coefficients from a distinct polynomial

$$f(x)=u_1{x}^{M-1}+u_2{x}^{M-2}+\dots +u_M$$

arranged in order of descending exponents u₁, u₂, ..., u_M. The polynomial has an order of M − 1 and contains positive integer exponents.

The block always treats a length-M unoriented vector input as an M-by-1 matrix.

Data Types: single | double
Complex Number Support: Yes

Output

Output — Polynomial stability test output

scalar | 1-by-N matrix

Polynomial stability test output, returned as a scalar or a 1-by-N matrix with each column containing the value 1 or 0.

The value of 1 indicates that the polynomial in the corresponding column of the input is stable, that is, the magnitudes of all solutions to f(x) = 0 are less than 1. The value of 0 indicates that the polynomial in the corresponding column of the input might be unstable, that is, the magnitude of at least one solution to f(x) = 0 is greater than or equal to 1.

Data Types: Boolean

Parameters

Simulate using — Type of simulation to run

Interpreted execution (default) | Code generation

Specify the type of simulation to run. You can set this parameter to:

• Interpreted execution — Simulate model using the MATLAB interpreter. This option shortens startup time.

• Code generation — Simulate model using generated C code. The first time you run a simulation, Simulink^® generates C code for the block. The C code is reused for subsequent simulations as long as the model does not change. This option requires additional startup time but provides faster subsequent simulations.

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Programmatic Use: Add Block

To add the block programmatically, use the add_block function with one of these library block paths as the source.

"dsppolyfun/Polynomial Stability Test"

Example: add_block("dsppolyfun/Polynomial Stability Test","myModel/myBlock",MakeNameUnique="on")

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Generated code relies on the memcpy or memset function (string.h) under certain conditions.

Version History

Introduced before R2006a