% Problem 4a

% Gather elevations in $ev$
  n = 0;                                % count of elevations so far
  e = input('Enter an elevation: ');    % enter first elevation
  while(e >= 0)                         % must enter only positive elevations
     n = n+1;	                        % increment count
     ev(n) = e;                         % store elevations in $ev$
     e = input('Enter an elevation: '); % process next input
  end

% Stop execution if no elevations entered
  if n==0
     disp(['Instituting instructor\'s perogative to use evil code.'])
     break
  end

% Subtract the elevation vector from itself such that the resulting vector $g$:
% + stores the entire vector of gradients
% + contains one less element than L
% Remember to assume constant spacing between measurements. 
% Use the $abs$ function to ensure all gradients in $g$ are positive

  g = abs( ev(2:n) - ev(1:n-1) )
%     ^^^  ^^^^^^^   ^^^^^^^^^

% Alternatives:
  g1 = abs(ev(2:n) - ev(1:n-1))
  g2 = abs(ev(1:n-1) - ev(2:n))

% Report maximum value inside $g$

  max(g)
% ^^^ ^  

% Plot elevations

  plot(ev)
%      ^^