function s = e11v1(m)
% s = e11v1(m): return a $m$-by-$2m$ string matrix $s$ with
% + $*$s on the border (left, right, top, and bottom edges)
% + $\$s on the diagonal, except for on the border
%   (the *diagonal* of a matrix = all valid positions (i,i) in the matrix)
% + $-$s below the diagonal, except for on the border
% + $+$s on the boundary, $@$s in the interior, and $c$ at the center of
%   a disk of radius $round(m*.35)$ and center $(round(m*1.5),round(m/2))$
%
% concise version using trick of logical arrays and coordinate matrices

n = 2*m; % width of $s$             % [3/14] fixed typo below, where $xc<-->yc$
xc = round(m*1.5); yc = round(m/2); % (yc,xc) = center of disk
r = round(m*.35);                   % radius of disk

% $x$, $y$: very useful for vectorization bonus, but probably no help otherwise
    y = repmat((1:m)', 1, n);       % y(i,j) = i = the row position (i,j) is in
    x = repmat(1:n, m, 1);          % x(i,j) = j = the col position (i,j) is in

s(m,n) = ' '; % make $s$ large enough
s(:,:) = 'o'; % fill each element with $'o'$

s(x < y) = '-';                         % place $-$s below diagonal
s(x == y) = '\';                        % place $\$s on diagonal
s([1 end],:) = '*'; s(:,[1 end]) = '*'; % place $*$s on border
d = sqrt((x-xc).^2 + (y-yc).^2);        % distances to center of disk
s(d < r) = '@';                         % place $@$s inside disk
s(abs(d-r)<.5) = '+';                   % place $+$s on disk 

s(yc, xc) = 'c';                        % place $c$ at center of disk