Descriptor State-Space

Model linear implicit systems

Since R2018b

• 

Libraries:
Simulink / Continuous

Description

The Descriptor State-Space block allows you to model linear implicit systems that can be expressed in the form$$E\dot{x}=Ax+Bu$$ where E is the mass matrix of the system. When E is nonsingular and therefore invertible, the system can be written in its explicit form $$\dot{x}=E^{-1}Ax+E^{-1}Bu$$ and modeled using the State-Space block.

When the mass matrix E is singular, one or more derivatives of the dependent variables of the system are not present in the equations. These variables are called algebraic variables. Differential equations that contain such algebraic variables are called differential algebraic equations. Their state space representation is of the form

$$\begin{array}{c}E\dot{x}=Ax+Bu\\ y=Cx+Du\end{array}$$

where the variables have the following meanings:

• x is the state vector

• u is the input vector

• y is the output vector

Examples

Model a Series RLC Circuit

Descriptor State-Space Example

Open Model

Ports

Input

Input 1 — Input signal

scalar | vector

Real-valued input vector of type double whose width is the number of columns in the B and D matrices.

Data Types: double

Output

Output 1 — Output vector

scalar | vector

Real-valued input vector of type double whose width is the number of rows in the C and D matrices.

Data Types: double

Parameters

E — Mass matrix

1 (default) | scalar | matrix

Specify the mass matrix E as a real-valued n-by-n matrix, where n is the number of states in the system. E must be the same size as A. E can be singular or non-singular.

Programmatic Use

Block Parameter: E

Type: character vector, string

Values: scalar | matrix

Default: '1'

A — Matrix coefficient, A

1 (default) | scalar | matrix

Specify the matrix coefficient A as a real-valued n-by-n matrix, where n is the number of states in the system. A must be the same size as E.

Programmatic Use

Block Parameter: A

Type: character vector, string

Values: scalar | matrix

Default: '1'

B — Matrix coefficient, B

1 (default) | scalar | vector | matrix

Specify the matrix coefficient B as a real-valued n-by-m matrix, where n is the number of states in the system and m is the number of inputs.

Programmatic Use

Block Parameter: B

Type: character vector, string

Values: scalar | vector | matrix

Default: '1'

C — Matrix coefficient, C

1 (default) | scalar | vector | matrix

Specify the matrix coefficient C as a real-valued r-by-n matrix, where n is the number of states in the system and r is the number of outputs.

Programmatic Use

Block Parameter: C

Type: character vector, string

Values: scalar | vector | matrix

Default: '1'

D — Matrix coefficient, D

1 (default) | scalar | vector | matrix

Specify the matrix coefficient D as a real-valued r-by-m matrix, where r is the number of outputs of the system and m is the number of inputs to the system.

Programmatic Use

Block Parameter: D

Type: character vector, string

Values: scalar | vector | matrix

Default: '1'

Initial condition — Initial condition of states

0 (default) | scalar | vector | matrix

Specify initial condition of the block states. The minimum and maximum values are bound by the Output minimum and Output maximum block parameters.

Tip

Simulink^® software does not allow the initial condition of this block to be inf or NaN.

Dependencies

To enable this parameter, set the Initial condition source to internal.

Programmatic Use

Block Parameter: InitialCondition

Type: character vector, string

Values: scalar | vector | matrix

Default: '0'

Direct feedthrough — Set output signal dependency on input

true (default) | false

Specify whether the output of the block has a direct dependency on the input signal. Use this parameter for systems having more than 500 continuous states in order to speed up simulation. For systems with 500 continuous states or less, Simulink automatically determines this setting.

Programmatic Use

Block Parameter: DirectFeedthrough

Type: character vector, string

Values: 'True' | 'False'

Default: 'True'

Linearize to sparse model — Linearize states to sparse matrices

on (default) | off

For Simulink Control Design™ workflows, linearize the system represented by the Descriptor State-Space block to a sparse model during linearization.

Disable this parameter to linearize the system to a non-sparse explicit state-space model.

Absolute tolerance — Absolute tolerance for computing block states

auto (default) | scalar | vector

Absolute tolerance for computing block states, specified as a positive, real-valued, scalar or vector. To inherit the absolute tolerance from the Configuration Parameters, specify auto or -1.

• If you enter a real scalar, then that value overrides the absolute tolerance in the Configuration Parameters dialog box for computing all block states.

• If you enter a real vector, then the dimension of that vector must match the dimension of the continuous states in the block. These values override the absolute tolerance in the Configuration Parameters dialog box.

• If you enter auto or –1, then Simulink uses the absolute tolerance value in the Configuration Parameters dialog box (see Solver Pane) to compute block states.

Programmatic Use

Block Parameter: AbsoluteTolerance

Type: character vector, string

Values: 'auto' | '-1' | any positive real-valued scalar or vector

Default: 'auto'

State Name (e.g., 'position') — Assign unique name to each state

' ' (default) | 'position' | {'a', 'b', 'c'} | a | ...

Assign a unique name to each state. If this field is blank (' '), no name assignment occurs.

• To assign a name to a single state, enter the name between quotes, for example, 'position'.

• To assign names to multiple states, enter a comma-delimited list surrounded by braces, for example, {'a', 'b', 'c'}. Each name must be unique.

• To assign state names with a variable in the MATLAB^® workspace, enter the variable without quotes. A variable can be a character vector, string, cell array, or structure.

Limitations

• The state names apply only to the selected block.

• The number of states must divide evenly among the number of state names.

• You can specify fewer names than states, but you cannot specify more names than states.

  For example, you can specify two names in a system with four states. The first name applies to the first two states and the second name to the last two states.

Programmatic Use

Block Parameter: ContinuousStateAttributes

Type: character vector, string

Values: ' ' | user-defined

Default: ' '

Block Characteristics

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

Extended Capabilities

C/C++ Code Generation

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

1. Consider using the Model Discretizer to map these continuous blocks into discrete equivalents that support code generation. To access the Model Discretizer, in the Apps tab, under Control Systems, click Model Discretizer.

2. Not recommended for production code.

Version History

Introduced in R2018b