How to solve the AX=0, When some of the elements in matrix X is known.

Question

JITHA K R 2018-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/376607-how-to-solve-the-ax-0-when-some-of-the-elements-in-matrix-x-is-known

评论： Luke Pretzie 2019-9-2

I have to solve for X. Equation is AX=0. A MATRIX is a square matrix and in X matrix some of the elements are known some are unknowns. I want to get the unknowns. Can someone help me?

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Answer 1

Birdman 2018-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/376607-how-to-solve-the-ax-0-when-some-of-the-elements-in-matrix-x-is-known#answer_299584

编辑：Birdman 2018-1-11

在 MATLAB Online 中打开

One approach is symbolical(requires Symbolic Toolbox).

A=[1 2 3;4 5 6;7 8 9];%dummy data
syms x1 x2
X=[x1;x2;1];
eq=A*X==0;
solx=solve(eq);
x1=solx.x1
x2=solx.x2

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JITHA K R 2018-1-11

How will I specify matrix X with some known values and other unknown values as symbolic variables.?

Birdman 2018-1-11

在 MATLAB Online 中打开

a=randi([1 10],18,1);%known dummy data
X=[x;a]

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Answer 2

Fadhel Alsaffar 2019-2-3

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https://ww2.mathworks.cn/matlabcentral/answers/376607-how-to-solve-the-ax-0-when-some-of-the-elements-in-matrix-x-is-known#answer_359230

I tried the code above with my matrix but it did not work

A=[0.6485 -1 0;-1 2.4728 -2;0 -2 4.2970];%dummy data

syms x1 x2

X=[x1;x2;1];

eq=A*X==0;

solx=solve(eq);

x1=solx.x1

x2=solx.x2

Do you know what the problem with my code?

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Luke Pretzie 2019-9-2

Did your code give you an error message? Or did it show no output, or it showed x1 and x2 as "structs"? You can convert your structs to floats using the double() function:

x1 = double(solx.x1)

x2 = double(solx.x2)

That's assuming, of course, that everyone else went right and you didn't get an error message. If you did, please let me know what it was. If not, let me know if my suggestion helped.

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