Algebraic Constraint

Purpose

Enforce an algebraic constraint by solving a system of equations

Library

Control / Math

Description

The Algebraic Constraint block outputs the value that produces zero at the input. The output must affect the input by means of a direct feedthrough path. The block ensures that the input signal is zero at all times.

The direct feedthrough path defines a function \(f\) of the output signal \(x\). The Algebraic Constraint block solves the system of equations \(f(x)=0\). The input and output signals must have the same width, i.e. the number of equations must equal the number of unknowns.

Note

The Algebraic Constraint block creates an algebraic loop. See section Block Sorting for more information on algebraic loops.

Example Model

• See the example model “Algebraic Constraint”.

• Find it in PLECS under Help > PLECS Documentation > List of Example Models.

Parameters

Initial guess

A guess of the solution \(x\) at the start of the simulation. The parameter can be either a scalar or a vector with the same width as the output and input signals. If a scalar is specified, the value is used as an initial guess for all components of the output signal. The default is 0.

Probe Signals

Residual

The constraint residual \(f\).

Solution

The computed solution \(x\).