Simple MATLAB sum question.

I am running a very old MATLAB 6.1. Anyways, I am have:

Ax=b
A=[a11 a12 a13;
a21 a22 a23;
a31 a32 a33]
x=[x1;
x2;
x3]

I want to write a MATLAB program that simply calculates:

b1=x1*a11+x1*a12+x1*a13
...

And the current code I have:

b(1:n,1)=zeros(n,1);
for j=1:n
   b(j,1)=x(j,1)*A(1,j)
end

Does not work. I have tried adding a nested for loop. No luck. I have tried the sum command. No luck.

Basically I want to do:

sum(A(1,:)+A(2,:)+...+A(j,:))

In a controlled loop sequence. I have tried:

for j=1:n
  sum(A(j,:))
end

Answer 1

[Walter Roberson]

Have you tried sum(A(1:j,:),2) ? I am referring to your "Basically I want to do" portion of your question, which otherwise appears to be incomplete in that it does not have the multiplication by b .

Does your version of Matlab not support matrix multiplication,

b = A*x;

Answer 2

[Matt Fig]

Is this what you are after?

b = zeros(3,1);
for ii = 1:3
    for jj = 1:3
        b(ii)= b(ii) + A(ii,jj)*x(jj);
    end
end