Matrix Multiplication with large vectors
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Hi,
If I have following problem how can I formulate it in matlab
A=
1 3
2 4
b=
xi
yi
where xi and yi are column vectors with lets say 100 values in each how can I input this problem in Matlab by using following formula
[z1 = A*b
z2]
Please note I have very large martix with vectors xi and yi and I want out put two matrices z1 and z2
Thanks in advance, jay
thanks
3 个评论
Walter Roberson
2015-5-11
Is the number of rows in A the same as the number of elements in xi and yi?
Are you looking for
z1 = A(:,1) .* xi;
z2 = A(:,2) .* yi;
?
amberly hadden
2015-5-11
编辑：Walter Roberson
2015-5-11
Walter Roberson
2015-5-11
There seems to be some confusion about whether xi and yi are row vectors or column vectors. You said column vectors before, but [xi;yi] would create a single column vector of the two combined, with [xi,yi] producing two columns from two column vectors.
采纳的回答
Walter Roberson
2015-5-15
T = arrayfun(@(x,y) A*[x;y], xi, yi, 'Uniform', 0);
z1z2 = vertcat(T{:});
z1 = z1z2(:,1);
z2 = z1z2(:,2);
However, this formulation of the code would not be efficient if you had a small A and long vectors. In your actual situation, what size() is your A ?
2 个评论
amberly hadden
2015-5-15
Walter Roberson
2015-5-15
In the case of A being 2 x 2, it is faster just to write out the values
z1 = A(1,1) * xi + A(2,1) * yi;
z2 = A(1,2) * xi + A(2,2) * yi;
更多回答（1 个）
A = [1 2; 3 4];
xi = 10;
yi = 20;
x = [xi; yi];
z1 = A(1,:)*x;
z2 = A(2,:)*x;
or
z = A*x;
z1 = z(1);
z2 = z(2);
1 个评论
amberly hadden
2015-5-15
编辑：Walter Roberson
2015-5-15
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