COMSOL Multiphysics™

femstate
Purpose
femstate
Compute state-space form of a time-dependent PDE problem.
Syntax
Description
[A,B,C,D] = femstate(fem,...)
[M,MA,MB,C,D] = femstate(fem,...)
[M,MA,MB,C,D,Null,ud,x0] = femstate(fem,...)
state = femstate(fem,...)
[A,B,C,D] = femstate(fem,...) calculates the linearized state-space form of the
dynamic PDE model fem on the format
⎧dx
⎪ = Ax + Bu
⎨dt
⎪
⎩ y = Cx+
Du
where x are the state variables, u are the input variables, and y are the output
variables.
[M,MA,MB,C,D] = femstate(fem,...) calculates the state-space form on the
format
⎧
⎪
⎨
⎪
⎩
dx
M dt
= MAx + MBu
y = Cx+
Du
The matrices M and MA are usually much sparser than the matrix A.
[M,MA,MB,C,D,Null,ud,x0] = femstate(fem,...) also returns the null space
matrix Null, the constraint contribution ud, and the initial state x0. The full
solution vector U can be obtained from the state variables by U = Null*x+u0, where
u0 is the linearization point.
state = femstate(fem,...) returns the structure state containing the fields M,
MA, MB, C, D, Null, and x0.
state = femstate(fem,'out','statenom',...) returns the structure state
containing the fields A, B, C, D, Null, and x0.
s = femstate(fem,'out','ss',...) returns the Control System Toolbox
state-space object s = ss(A,B,C,D).
The output from femstate is intended for use from Simulink or the Control System
Toolbox. The function femstate with the output state is equivalent to femsim
162 | CHAPTER 1: COMMAND REFERENCE