Extract values from one matrix and with iteration solve the system of linear equations

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Alina Abdikadyr
Alina Abdikadyr 2022-10-3
评论： Alina Abdikadyr 2022-10-4
Hello everyone!
Please, help me write a code for solving the system of linear equations in Matlab
If I have a column of coefficients A [A1;A2;A3] and the inverse matrix 3x3 B^(-1) and unknown column C [C1, C1, C1] (here all values are equal)
I have to find C1 value and plot the graph. Also A1 values can be extraacted from another matrix, so unknowns are A2, A3 and C1
A.'*B^(-1) = C

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回答（2 个）

Walter Roberson
Walter Roberson 2022-10-3
Ran in:
A = randi([-5 5], 5 ,3)
A = 5×3
0 -4 -5 5 3 -4 -1 -1 0 4 3 -5 5 4 -4
B = randi(9,3, 3)
B = 3×3
4 8 7 1 1 9 9 6 1
C = A/B
C = 5×3
-0.7494 -0.0098 0.3342 -0.0319 -0.4889 0.6241 -0.0663 0.0614 -0.0885 0.1057 -0.6904 0.4742 0.1646 -0.6339 0.5528
plot(C(:,1))
Torsten
Torsten 2022-10-4
编辑：Torsten 2022-10-4
Ran in:
B = rand(3,3);
A1 = 4;
rhs = -A1*B(1,:).';
Mat = [-ones(3,1),B(2:3,:).'];
sol = Mat\rhs;
C1 = sol(1)
C1 = 9.4544
A2 = sol(2)
A2 = 80.7027
A3 = sol(3)
A3 = -250.8747
[A1 A2 A3]*B-[C1 C1 C1]
ans = 1×3
1.0e-14 * -0.3553 -0.3553 -0.7105
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Torsten
Torsten 2022-10-4
Ran in:
Use a loop:
B = rand(3,3);
A1 = [4,pi,-80,329];
C1 = zeros(size(A1));
A2 = zeros(size(A1));
A3 = zeros(size(A1));
for i=1:numel(A1)
rhs = -A1(i)*B(1,:).';
Mat = [-ones(3,1),B(2:3,:).'];
sol = Mat\rhs;
C1(i) = sol(1);
A2(i) = sol(2);
A3(i) = sol(3);
[A1(i) A2(i) A3(i)]*B-[C1(i) C1(i) C1(i)];
end
C1 = 1×4
-10.8402 0 0 0
A2 = 1×4
-19.4251 0 0 0
A3 = 1×4
-0.3832 0 0 0
ans = 1×3
1.0e-14 * -0.1776 -0.1776 0
C1 = 1×4
-10.8402 -8.5139 0 0
A2 = 1×4
-19.4251 -15.2565 0 0
A3 = 1×4
-0.3832 -0.3009 0 0
ans = 1×3
1.0e-14 * 0 -0.1776 -0.1776
C1 = 1×4
-10.8402 -8.5139 216.8035 0
A2 = 1×4
-19.4251 -15.2565 388.5023 0
A3 = 1×4
-0.3832 -0.3009 7.6631 0
ans = 1×3
1.0e-13 * -0.2842 -0.2842 0
C1 = 1×4
-10.8402 -8.5139 216.8035 -891.6043
A2 = 1×4
1.0e+03 * -0.0194 -0.0153 0.3885 -1.5977
A3 = 1×4
-0.3832 -0.3009 7.6631 -31.5146
ans = 1×3
1.0e-12 * 0 0 -0.1137

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