How to make a symmetric matrix with symbolic elements

Question

Bill Tubbs 2020-5-28

评论： Bill Tubbs 2020-5-31

There's already a similar question for how to make a symmetric matrix with certain values.

But I want to create a symbolic matrix that is symmetric.

I learned how to make a non-symmetric symbolic matrix thus:

>> n=3;
>> Q = sym('q', [n n])
Q =
 
[ q1_1, q1_2, q1_3]
[ q2_1, q2_2, q2_3]
[ q3_1, q3_2, q3_3]

Now I want to know if there is an easy way to make this:

Q =
 
[ q1_1, q1_2, q1_3]
[ q1_2, q2_2, q2_3]
[ q1_3, q2_3, q3_3]

Bill Tubbs 2020-5-31

Just realized this question has already been asked and answered here.

Answer 1

Bill Tubbs 2020-5-28

编辑：Bill Tubbs 2020-5-28

This seems to work:

>> Q = tril(Q.') + triu(Q,1)  % Uses top half of Q to make Q symmetric
 
Q =
 
[ q1_1, q1_2, q1_3]
[ q1_2, q2_2, q2_3]
[ q1_3, q2_3, q3_3]