doc: Review and update documentation for "Matrix Manipulation" chapter. * matrix.txi, arrayfun.m, blkdiag.m, fliplr.m, flipud.m, logspace.m, postpad.m, prepad.m, randi.m, repmat.m, rot90.m, rotdim.m, shiftdim.m, sortrows.m, vech.m, xor.m, hadamard.m, hankel.m, hilb.m, invhilb.m, magic.m, pascal.m, rosser.m, sylvester_matrix.m, toeplitz.m, vander.m, wilkinson.m, bsxfun.cc, find.cc, lookup.cc, rand.cc, tril.cc, data.cc, arrayfun.m, blkdiag.m, fliplr.m, flipud.m, logspace.m, postpad.m, prepad.m, randi.m, repmat.m, rot90.m, rotdim.m, shiftdim.m, sortrows.m, vech.m, xor.m, hadamard.m, hankel.m, hilb.m, invhilb.m, magic.m, pascal.m, rosser.m, sylvester_matrix.m, toeplitz.m, vander.m, wilkinson.m, bsxfun.cc (bsxfun), find.cc (find), lookup.cc (lookup), rand.cc (rand, randn, rande, randg, randp), tril.cc (triu), data.cc (all, any, horzcat, vertcat, cat, permute, ipermute, ones, zeros, eye, linspace, resize, reshape, issorted, diff): Improve docstrings

--- a/scripts/special-matrix/magic.m
+++ b/scripts/special-matrix/magic.m
@@ -19,9 +19,11 @@
 ## -*- texinfo -*-
 ## @deftypefn {Function File} {} magic (@var{n})
 ##
-## Create an @var{n}-by-@var{n} magic square.  Note that @code{magic
-## (@var{2})} is undefined since there is no 2-by-2 magic square.
+## Create an @var{n}-by-@var{n} magic square.  A magic square is an arrangement
+## of the integers @code{1:n^2} such that the row sums, column sums, and
+## diagonal sums are all equal to the same value.
 ##
+## Note: @var{n} must be greater than 2 for the magic square to exist.
 ## @end deftypefn
 
 function A = magic(n)