State space without using the control toolbox - Error using + Matrix dimensions must agree.

3 次查看（过去 30 天）
George Green
George Green 2015-5-28
编辑： George Green 2015-5-29
I am trying to calculate a continous plant for a unit step input.
Eg dX/dt= AX * Bu y = CX
I get the following error: Error using + Matrix dimensions must agree.
Can anyone please assist me??
My code is below:
%%Time specifications
stopTime = 10;
Fs = 1;
dt = 1/Fs;
t = (0:dt:stopTime)';
N = size(t,1);
%%State space model
A = [0,1;-45,-876];
B = [0,0;1,1]; %Rev 3
C = [59 99];
%%Pre-allocation
u = zeros(2,N);
x = zeros(2,N); %Rev 1
y = zeros(2,N);
%%Initial conditions
u(:,1) = [ 1 ; 1 ];
x(:,1) = [ 0 ; 0 ]; % Rev 1
y(:,1) = [ 0 ; 0 ];
%%Simulation - main loop
for k = 2:N
x(:,k) = x(:,k-1) + dt.*(A*x(:,k-1) + B*u(:,k-1); % Rev 2
y(:,k) = C*x(:,k);
end
%%Plot results
figure;
ax(1) = subplot(2,1,1);
plot(t,x);
ax(2) = subplot(2,1,2);
plot(t,y);
linkaxes(ax,'x');

请先登录，再回答此问题。

回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2015-5-28
The matrix A is 2x2 then x should be 2x1 not 3x1
  1 个评论
George Green
George Green 2015-5-29
编辑：George Green 2015-5-29
Hi Azzi,
I correct the errors above for x (Rev 1) however I still get:
Error using + Matrix dimensions must agree.
Error in (line 28) x(:,k) = x(:,k-1) + dt*(A*x(k-1) + B*u(k-1));
Your suggestions would be much appreciated.

请先登录，再进行评论。

Nobel Mondal
Nobel Mondal 2015-5-29
In this line,
x(:,k) = x(:,k-1) + dt*(A*x(k-1) + B*u(k-1)); % Error
The term A*x(k-1) would give you a 2x2 matrix. You should be using x(:,k-1) instead.
x(:,k) = x(:,k-1) + dt*(A*x(:,k-1) + B*u(k-1));
  1 个评论
George Green
George Green 2015-5-29
Thanks for your help Nobel,
Thats what I meant to do but bit of an oversight on my part. I made the changes (Rev2) but got: " Error using * Inner matrix dimensions must agree." for x(:,k) = x(:,k-1) + dt.(A*x(:,k-1) + B*u(:,k-1));"
I then changed B from " B = [0;1] " to " B = [0 0 ;1 1] " ....Does this look right?

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by