Halley
Posts:
5
Registered:
10/20/11


Re: Matrix dimensions must agree
Posted:
Oct 20, 2011 12:12 PM


"Halley" wrote in message <j7pgmh$egc$1@newscl01ah.mathworks.com>... > "Matt J" wrote in message <j7pf7q$9b3$1@newscl01ah.mathworks.com>... > > "Halley" wrote in message <j7pdmt$3o9$1@newscl01ah.mathworks.com>... > > > > > > %Calculate old values > > > rho(i) = (x_a(i,:).*A.*x(:,i))./(x_a(i,:).*B.*x(:,i)) > > ======== > > > > I suspect you mean to do * instead of .* > > > > In any case, the sizes definitely aren't compatible for the .* operation > > I think this is the simplest solution, thanks.
I had actually been toying with that solution as I waited for responses when I ran across a new problem. With each iteration my values are not changing. As I mentioned, x(i) should become xnorm(i) and rho(i) should equal rho(i+1). I suspect that this is the problem, that somehow the order of the operations regarding rho is making it so that the relative error doesn't change. I have tried taking rho(i) out of the loop and calculating rho(1) but that did not seem to help either. I've been struggling with these problems for a few days so the help is really appreciated.
%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 return elseif (relative_error == 0) x(:,i) = xnorm(:,i) rho(i) = rho(i+1) k = k+1 elseif (relative_error > TOL) x(:,i) = xnorm(:,i) rho(i) = rho(i+1) k = k+1 end end

