How to create a symbolic matrix which is symmetric?

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Will Bolton
Will Bolton 2018-3-1
评论： Walter Roberson 2018-3-1
Hello, I essentially want to create something with the form you would get from doing:
A = sym('A', [6,6])
but additionally I would like A to be symmetric and I'm not sure if there is an easy way to generate this?

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John D'Errico
John D'Errico 2018-3-1
编辑：John D'Errico 2018-3-1
A = sym('A', [6,6]);
A = tril(A,0) + tril(A,-1).'
A =
[ A1_1, A2_1, A3_1, A4_1, A5_1, A6_1]
[ A2_1, A2_2, A3_2, A4_2, A5_2, A6_2]
[ A3_1, A3_2, A3_3, A4_3, A5_3, A6_3]
[ A4_1, A4_2, A4_3, A4_4, A5_4, A6_4]
[ A5_1, A5_2, A5_3, A5_4, A5_5, A6_5]
[ A6_1, A6_2, A6_3, A6_4, A6_5, A6_6]
Looks symmetric to me.
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Will Bolton
Will Bolton 2018-3-1
Hmm so now I have the issue with this method that if I want to solve with this matrix, when I plug it back in I get the error:
One or more variables are used multiple times. Cannot distinguish between variables and equations. Use a vector of equations and a vector of variables to avoid ambiguity.
I essentially have a system of equations in the lower triangle of a matrix, with the upper portion all zeroes. I am trying to solve in terms of the elements of the symmetric matrix. There are the same number of variables as there are equations but what I'm trying isn't working. I have tried:
sol = solve(eqn, W)
sol = solve(eqn, tril(W))
The former gets the error above, the latter gets:
The second argument must be a vector of symbolic variables.

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