I fixed several issues. The biggest one is that
zeros(N)
will create and NxN array, not an Nx1 array. So, I assume you wanted
sumxy=zeros(length(x),1);
etc.
Next, I changed
sumxy(i)=sumxy+(x(i).*y(i));
to
sumxy(i)=sumxy(i)+(x(i).*y(i));
because I assume that's what you intended.
Finally, in the last two lines, I added more element-wise operations.
In the end, it runs. I have no idea if it does what you intend.
function [m,b] = Problem5_18(x,y)
%Problem5_18 Linear Least-Squares Fit.
%This function calculates slope m and intercept b of the least-squares line
%that best fits an input dataset.
narginchk(2,2);
if nargout<2
m='Make sure that you ask for both outputs!';
warning(m);
end
if length(x)~=length(y)
n='Check your inputs; input arrays must be of the same length!';
error(n);
end
sumxy=zeros(length(x),1);
sumx=zeros(length(x),1);
sumy=zeros(length(x),1);
sumx2=zeros(length(x),1);
for i=1:length(x)
sumxy(i)=sumxy(i)+(x(i)*y(i));
sumx(i)=sumx(i)+x(i);
sumy(i)=sumy(i)+y(i);
sumx2(i)=sumx2(i)+(x(i)^2);
end
ybar=sumy/length(x);
xbar=sumx/length(x);
m=(sumxy-(sumx.*ybar))./(sumx2-(sumx.*xbar));
b=ybar-(m.*xbar);
