lower diagonal matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg80391] lower diagonal matrix*From*: Sean Bonness <nbonness at chem.ucsb.edu>*Date*: Tue, 21 Aug 2007 05:01:06 -0400 (EDT)

Hello... I am in need of some help in trying to convert data I got from another program into mathematica so that I can eventually diagonalize the matrix. What I have from the other program are values for a lower diagonal matrix, which corresponds to a full symmetric matrix and whereby the program tries to save on writing alot of data by just writing the lower diagonal matrix. The values I have from another program are in a five column by 56 row matrix. The first element (1,1) in this matrix corresponds to the (1,1) element in a lower diagonal matrix, the second element (1,2) corresponds to (2,1), the third (1,3) corresponds to (2,2), the fourth (1,4) corresponds to (3,1), the fifth (1,5) corresponds to (3,2), the sixth (2,1) corresponds to (3,3) and so on. What I have done so far is read in the data into mathematica, but when I do it reads it in as a one dimensional list. What I would like to do is to break up the data into a human readable form of a lower diagonal matrix and then construct a full symmetric (23x23) matrix of this data so as to eventually diagonalize and solve it. The lower diagonal elements are the same as the upper diagonal elements, so I understand that I would need to specify the elements to be a[i,j]=a[j,i] somewhere in defining the symmetric matrix. Any help in trying to help me write/ construct the full symmetric matrix from the data I have would be much appreciated.