Simple MATLAB sum question.

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Myles Baker
Myles Baker 2011-1-21
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

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回答（2 个）

Walter Roberson
Walter Roberson 2011-1-21
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;
Matt Fig
Matt Fig 2011-1-21
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

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