Why wont these matrices multiply

xo = [1; 2; 3; 4; 5; 6];

n = 7;

t = 0:15:2700 

for i=length(t)

phi = [4-3*cos(n*t(i)) 0 0 sin(n*t(i))/n 2*(1-cos(n*t(i)))/n 0; 6*(sin(n*t(i))-n*t(i)) 1 0 2*(cos(n*t(i))-1)/n (4*sin(n*t(i))-3*n*t(i))/n 0; 0 0 cos(n*t(i)) 0 0 sin(n*t(i))/n; 3*n*sin(n*t(i)) 0 0 -2*sin(n*t(i)) 4*cos(n*t(i))-3 0; 0 0 -n*sin(n*t(i)) 0 0 cos(n*t(i))]

x(i) = phi*xo %This is where I am getting the error

end

I am trying to compute the Hill Clohessy Wiltshire equations for the given t, n, xo, and phi values.

The equation is x(t) = phi(t)*xo.

I am getting and error where x(i)=phi*xo that says

Subscripted assignment dimension mismatch.'

... when I do it outside of the for statement it works fine, but since I need to compute this for multiple ts i figured i would have to use a for statement. I am not very familer with matlab so please explain it to me as explicitly as you can.

Answer 1

[Walter Roberson]

Your phi creates a 5 x 6 matrix, which you then multiply by the 6 x 1 matrix x0. Algebraic matrix multiplication is used because you used the "*" operator. The result is going to be 5 x 1. You are trying to store the 5 x 1 array into a single memory location x(i).

I suggest you change

x(i) = phi * x0;

to

x(:,i) = phi * x0;

The result would then be a 5 x length(t) array in which the K'th column would correspond to t(K)

Answer 2

[Image Analyst]

phi is a 5 by 6 array. xo is a 6 by 1 array. The matrix product is a 5 by 1 column vector. Yet you're trying to stuff it into x(i) which is a single element, not a 5 by 1 array.