writem is used to write a matrix to a file. The output is
intended to be compatible with both the readm function and
several other programs, such as MATLABTM, and spreadsheets.
Each line in the output file contains all the values for the
corresponding row in the matrix argument. The values within each line
are delimited by whitespace. writem will output all kinds of
matricies, but readm can only read numeric matricies with real
values.