The Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Math Forum » Discussions » Software » comp.soft-sys.matlab

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Matrix dimensions must agree
Replies: 7   Last Post: Oct 20, 2011 2:30 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]

Posts: 5
Registered: 10/20/11
Matrix dimensions must agree
Posted: Oct 20, 2011 11:11 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

I am trying to write a program that utilizes the inverse iterative method. I calculate an initial x value and rho value given the matrices A, B, and b. I calculate a value of x normalized to the matrix B (xnorm) as well as a new value for rho for each iteration. Given that the relative error of rho is less than my preset tolerance (TOL) the loop ends, otherwise xnorm becomes the new value for x and the rho(i+1) becomes rho(i). The problem is in calculating rho(i), I am told my matrix dimensions do not agree when I have checked the sizes multiple times. Any suggestions? Thanks.

%Declare initial variables
A = [2 -1;-1 4];
b = [1;1];
B = [1 0;0 1];
Nmax = 20;
TOL = 1*10^-5;
k = 1;
x = zeros(2,21);
x_a = zeros(21,2);
rho = zeros(21,1);
xnorm = zeros(2,21);
x(:,1) = A\b;
x_a(1,:) = x(:,1)'

for i =1:Nmax

%Calculate old values
rho(i) = (x_a(i,:).*A.*x(:,i))./(x_a(i,:).*B.*x(:,i))

%Calculate new values
xnorm(:,i) = (1/sqrt(x_a(i,:).*B.*x(:,i))).*x(:,i)
rho(i+1) = (x_a(i,:).*A.*x(:,i))./(x_a(i,:).*B.*x(:,i))

%Check for convergence
relative_error = abs((rho(i+1)-rho(i))/rho(i+1))

if ( relative_error ~= 0 && relative_error <= TOL )
x(i+1) = xnorm(i)
rho(i+1) = rho(i+1)
k = k
elseif (relative_error ~= 0 && relative > TOL)
x(i+1) = xnorm(i)
rho(i) = rho(i+1)
k = k+1


Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© The Math Forum at NCTM 1994-2018. All Rights Reserved.