matrix math problems , error in matrix size

1 view (last 30 days)
i have a rectangular matrix of size 18 by 3 and a column of 18 by 1, when I try to solve for the x matrix (3 by 1) it says I have incorrect sized dimensions to do the math, why? mat lab says the rows should agree and it should allow me to divide them using "/"
xx=[x_e; x_a; x_w];
NU=[lnu_e;lnu_a;lnu_w];
co=xx/NU;

Accepted Answer

Paul
Paul on 22 Oct 2022
Hard to say without without knowing anything about the data in the question. Based on the wording it should work as follows
A = rand(18,3); % 18 by 3
b = rand(18,1); % 18 by 1
x = A\b % solve for 3 x 1, note use of backslash
x = 3×1
0.5890 0.4314 0.1437
ans = 18×1
-0.1966 -0.0326 0.4505 0.0437 0.3522 -0.0633 -0.0692 -0.6059 -0.3226 -0.0753
The result does not satisfy the matrix equation because there are more equations than unknowns
norm(A*x - b)
See mldivide, \ for more info on how it treats this case.

More Answers (1)

Walter Roberson
Walter Roberson on 22 Oct 2022
xx = rand(18,3);
NU = rand(18,1);
try
xx/NU
fprintf('/ worked\n');
catch ME
fprintf('well, / did not work\n');
end
well, / did not work
try
xx\NU
fprintf('\\ worked\n');
catch ME
fprintf('well, \\ did not work\n');
end
ans = 3×1
0.4033 0.1974 0.1226
\ worked

Categories

Find more on Linear Algebra in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by