How to load this kind of matrix in MATLAB

Question

I have an upper triangular matrix like:

A=  load(\'A.txt\');

1.0    3.32   -7.23
       1.00    0.60
               1.00

I want t

Answer 1

Try using importdata instead, load is usually only used for .mat files. How is your file A.txt structured? If it is like this,

1.0    3.32   -7.23
1.00    0.60
1.00

then you will get

A = importdata('A.txt')

A =

    1.0000    3.3200   -7.2300
    1.0000    0.6000       NaN
    1.0000       NaN       NaN

So you will have to shift the two last rows, like this

A(2,:) = circshift(A(2,:),[0 1])
A(3,:) = circshift(A(3,:),[0 2])

A =

    1.0000    3.3200   -7.2300
    NaN       1.0000    0.6000
    NaN       NaN       1.0000

and then replace the NaNs with 0s and use your expression to create a symmetric matrix.

A(isnan(A)) = 0;

a = A + triu(A, 1)';

A =

    1.0000    3.3200   -7.2300
    3.3200    1.0000    0.6000
   -7.2300    0.6000    1.0000