Matrix dimensions must agree

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Meaghan
Meaghan on 17 Oct 2017
Answered: Gautam on 23 Oct 2024
Hi, I am having trouble with solving a system of linear equations. I am getting an error that the matrix dimensions must agree and i cannot divide a/b.
if true
x1=167.48;
x2 = 355.63;
x3 = 355.63;
x4=264.58;
x5=62.93;
x6=167.48;
a= 1000.*(6+.005.*x1)./1.1 ;
b= 1000.*(6+.005.*x2)./1.1 ;
c= 1000.*(6+.005.*x3)./1.1 ;
d= 1000.*(6+.005.*x4)./1.1 ;
e= 1000.*(6+.005.*x5)./1.1;
f= 1000.*(6+.005.*x6)./1.1;
g= (1000.*(6+.005.*x1)/1.1).^-1;
h= (1000.*(6+.005.*x2)/1.1).^-1;
i= (1000.*(6+.005.*x3)/1.1).^-1;
j=(1000.*(6+.005.*x4)/1.1).^-1 ;
k=(1000.*(6+.005.*x5)/1.1).^-1;
l=(1000.*(6+.005.*x6)/1.1).^-1 ;
r = -.0024
a = [1,0,0,0,0,0, 0,0,0,0,0,0, g,0,0,0,0,0 0,0,0,0,0,0;
0,1,0,0,0,0, 0,0,0,0,0,0, 0,h,0,0,0,0 0,0,0,0,0,0;
0,0,1,0,0,0, 0,0,0,0,0,0, 0,0,i,0,0,0 0,0,0,0,0,0;
0,0,0,1,0,0, 0,0,0,0,0,0, 0,0,0,j,0,0 0,0,0,0,0,0;
0,0,0,0,1,0, 0,0,0,0,0,0, 0,0,0,0,k,0 0,0,0,0,0,0;
0,0,0,0,0,1, 0,0,0,0,0,0, 0,0,0,0,0,l 0,0,0,0,0,0;
r,0,0,0,0,0 1,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0;
0,r,0,0,0,0 0,1,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0;
0,0,r,0,0,0 0,0,1,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0;
0,0,0,r,0,0 0,0,0,1,0,0 0,0,0,0,0,0 0,0,0,0,0,0;
0,0,0,0,r,0 0,0,0,0,1,0 0,0,0,0,0,0 0,0,0,0,0,0;
0,0,0,0,0,r 0,0,0,0,0,1 0,0,0,0,0,0 0,0,0,0,0,0;
0,0,0,0,0,0 a,0,0,0,0,0 0,0,0,0,0,0 1,0,0,0,0,0;
0,0,0,0,0,0 0,b,0,0,0,0 0,0,0,0,0,0 0,1,0,0,0,0;
0,0,0,0,0,0 0,0,c,0,0,0 0,0,0,0,0,0 0,0,1,0,0,0;
0,0,0,0,0,0 0,0,0,d,0,0 0,0,0,0,0,0 0,0,0,1,0,0;
0,0,0,0,0,0 0,0,0,0,e,0 0,0,0,0,0,0 0,0,0,0,1,0;
0,0,0,0,0,0 0,0,0,0,0,f 0,0,0,0,0,0 0,0,0,0,0,1;
0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0 1,0,0,0,0,-1;
0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0 0,1,0,0,0,-1;
0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0 0,0,1,0,0,-1;
0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,1,0,-1;
0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,0,0 0,0,0,0,1,-1;
0,0,0,0,0,0 0,0,0,0,0,0 1,1,1,1,1,1 0,0,0,0,0,0;];
% 1 2 3 4 5 6 7 8 9 101112131415161718192021222324
b = [0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;];
x= size(a)
z = size(b)
y = a/b
end

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Answers (2)

KSSV
KSSV on 17 Oct 2017
Replace:
y = a/b
with
y = a\b
Gautam
Gautam on 23 Oct 2024
Hello Meaghan,
The reason you get this error is because you cannot divide two matrices the way you divide two scalars.
To find the solution to a system of linear equations, use the “\” operation instead of “/”. Like, “y = a\b”
Hope this helps

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