How does lsim work?

Hye.

I've been trying to figure out how the lsim function works in MATLAB. Does it do a time domain solution or a frequency domain solution? I am basically trying to solve a transfer function using lsim. The solution works out perfectly fine, but I have been trying to understand the theory behind how it works. I am very new to MATLAB, so kindly explain the basics if you've got time. THanks

Answer 1

[Robert U]

Hi shahzer rahman,

your question is answered within Matlab documentation: lsim(), linking to ltitr() (which unfortunately does not have a documentation entry in the current version, built-in function, see below) and filter().

open ltitr

%LTITR	Linear time-invariant time response kernel.
%
%   X = LTITR(A,B,U) calculates the time response of the
%   system:
%           x[n+1] = Ax[n] + Bu[n]
%
%   to input sequence U.  The matrix U must have as many columns as
%   there are inputs u.  Each row of U corresponds to a new time 
%   point.  LTITR returns a matrix X with as many columns as the
%   number of states x, and with as many rows as in U.
%
%   LTITR(A,B,U,X0) can be used if initial conditions exist.
%   Here is what it implements, in high speed:
%
%	for i=1:n
%          x(:,i) = x0;
%          x0 = a * x0 + b * u(i,:).';
%	end
%	x = x.';

%	Copyright 1984-2007 The MathWorks, Inc.

% built-in function

Same question here: Matlab forum

Your core question answered short: lsim solves your system response in time domain.

Kind regards,

Robert

[shahzer rahman]

Thanks alot Robert. Appreciate the effort.