Solve linear equation in matrix form with least square method

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DoinK 2023-5-26

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https://ww2.mathworks.cn/matlabcentral/answers/1974114-solve-linear-equation-in-matrix-form-with-least-square-method

编辑： DoinK 2023-5-28

I have linear equation Ax=b, the size of every matrix are : matrix A is 1009*1008, vector b is 1009*1, and vector x is 1008*1.

If I use lsqr command which is lsqr(A,b), this come out

"Error using iterchk (line 38)

Argument must be a floating point matrix or a function handle.

Error in lsqr (line 93)

[atype,afun,afcnstr] = iterchk(A);".

If I try simple matrix, it can calculate easily.

If I use (A.'*A)\(A.'*b), i can get the result, but why this code lsqr(A,b) cannot

I want to know what is wrong and how to solve it.

Actually i have 1009 linear equation and 1008 variable, so i use this method, or is there any method to use to solve this problem?

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采纳的回答

Matt J 2023-5-26

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编辑：Matt J 2023-5-26

在 MATLAB Online 中打开

If I use (A.'*A)\(A.'*b), i can get the result

An even easier and more accurate way to get it is,

x=A\b

and that is the method you should be using for matrix data of this size. As to why you get the error, perhaps your A matrix is not type double, but some other type? E.g.,

A=randi(3,3,'int8'); 
b=A(:,1);
lsqr(double(A),double(b))
lsqr converged at iteration 3 to a solution with relative residual 2.9e-13.
ans = 3×1
    1.0000
   -0.0000
   -0.0000
lsqr(A,b)
Error using iterchk
Argument must be a floating point matrix or a function handle.

Error in lsqr (line 93)
[atype,afun] = iterchk(A);