squareform
              "tovector")"tomatrix")Interchange between distance matrix and distance vector formats.
Converts between an hollow (diagonal filled with zeros), square, and symmetric matrix and a vector with of the lower triangular part.
 Its target application is the conversion of the vector returned by
 pdist into a distance matrix.  It performs the opposite operation
 if input is a matrix.
 If x is a vector, its number of elements must fit into the
 triangular part of a matrix (main diagonal excluded).  In other words,
 numel (x) = n * (n - 1) / 2 for some integer
 n.  The resulting matrix will be n by n.
 If x is a distance matrix, it must be square and the diagonal entries
 of x must all be zeros.  squareform will generate a warning if
 x is not symmetric.
 The second argument is used to specify the output type in case there
 is a single element.  It will defaults to "tomatrix" otherwise.
See also: pdist
Source Code: squareform