How to reflect the element above the diagonal of a matrix to the lower diagonal ?

How could I reflect all the upper element of a square matrix of size K = 3 to the lower side

Like this ?

Thank you very much

Answer 1

[Matt J]

b=triu(a)+triu(a,1).'; %the result

[Tuong Nguyen Minh]

Why we use triu(a,1).' with the dot instead of triu(a,1)'

When I check it there was not much different, but is this dot usage a prefer engineering practice ?

[Matt J]

.' means transpose

https://www.mathworks.com/help/matlab/ref/transpose.html

Without the dot, it is conjugate tranpose

https://www.mathworks.com/help/matlab/ref/ctranspose.html

As long as your matrices are real-valued, they should give the same result.