# Sort an array of points to generate an envelope in MATLAB

I have the next vectors:

```A = [0;100;100;2100;100;2000;2100;2100;0;100;2000;2100;0];
B = [0;0;1450;1450;1550;1550;1550;1550;2500;2500;3000;3000;0]```

If we plot A and B, we'll obtain the following graphic: Then, I wonder how to short the points in order to have the next plot: As you can see, there're some conditions like: all of them form right angles; there's no intersection between lines.

This can be solved in the traditional recursive 'maze' solution of 'crawling on walls':

```%%% In file solveMaze.m
function Out = solveMaze (Pts,Accum)

if isempty (Pts); Out = Accum; return; end   % base case

x = Accum(1, end);  y = Accum(2, end);    % current point under consideration
X = Pts(1,:);       Y = Pts(2,:);         % remaining points to choose from

% Solve 'maze' by wall-crawling (priority: right, up, left, down)
if     find (X > x  & Y == y); Ind = find (X > x  & Y == y); Ind = Ind(1);
elseif find (X == x & Y > y ); Ind = find (X == x & Y > y ); Ind = Ind(1);
elseif find (X < x  & Y == y); Ind = find (X < x  & Y == y); Ind = Ind(1);
elseif find (X == x & Y < y ); Ind = find (X == x & Y < y ); Ind = Ind(1);
else error('Incompatible maze');
end

Accum(:,end+1) = Pts(:,Ind);    % Add successor to accumulator
Pts(:,Ind) = [];                % ... and remove from Pts

Out = solveMaze (Pts, Accum);
end```

Call as follows, given A and B as above;

```Pts = [A.'; B.']; Pts = unique (Pts.', 'rows').'; % remove duplicates
Out = solveMaze (Pts, Pts(:,1));                  % first point as starting point
plot(Out(1,:), Out(2,:),'-o');                    % gives expected plot```