How to tell if a random 3x3 Matrix is invertible
10 次查看(过去 30 天)
显示 更早的评论
I have to produce a random 3x3 matrix A that is invertible and display it. I have a couple questions:
- How do I know when a matrix is invertible? I used the command (inv) on the random 3x3 matrix that I had created and I got a 3x3 matrix with different numbers. Does this mean that the matrix is invertible?
- I also got a hint with the question: Use a while-loop until you get one with non-zero determinant. I am confused by this because I used the determinants command (det) on my 3x3 matrix and got a nonzero determinant. I feel like I might be missing something here.
2 个评论
Walter Roberson
2020-1-10
rank()
Most random matrices with floating point entries are invertible. Not all, but most. So unless you are using integer random values, do not be surprised if the first one you generate works.
采纳的回答
Meg Noah
2020-1-10
编辑:Meg Noah
2020-1-11
Back to your question, I have to produce a random 3x3 matrix A that is invertible and display it. One way could be to start with a matrix that you know will have a determinant of zero and then add random noise to each element. It worked for me to generate random matrices that are invertable.
for MC = 1:10000
% first create a matrix that you know has a low rcond value:
A = double(uint32(1000.*rand(3,1)).*uint32(1000.*rand(1,3)));
% then add noise
C = A + 100.0*rand(3,3);
if (rcond(C)<1e-20)
disp('algorithm fails');
C
inv(C)
end
end
There were objections to this suggestion about checking the determinant value. I had said: If the determinant of a square matrix is 0, it can't be inverted. I'd suggestion to test with - using your tolerance on the last argument. See comments below.
7 个评论
Steven Lord
2020-1-11
Better is simply to not invert a matrix. If you're trying to invert the matrix to solve a system of equations, use the backslash operator (\).
更多回答(0 个)
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Switches and Breakers 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!