% FUNCTION Y = EROSION(X, N_TIMES)

function y = erosion(x, n_times)

  if n_times < 0
    error( 'erosion needs n_times >= 0' );
  end
  
  siz = size( x );
  
  if sum( siz>1 ) > 1
    disp( 'erosion: WARNING! Input has more than one dimension.' );
  end
  
  if n_times < 1
    y = x;
    return;
  end
  
  x = x(:);
  
  % Mirror-replicate beginning and end of data vector
  
  n_left = min( length( x ), n_times );
  fill_left = x( n_left:-1:1 );
  fill_left = [ repmat( fill_left( 1 ), n_times-n_left, 1 );  fill_left ];
  
  n_right = min( length( x ), n_times );
  fill_right = x( end:-1:end-n_right+1 );
  fill_right = [ fill_right; repmat( fill_right( end ), n_times-n_right, 1 ) ];
  
  aux = [fill_left; x(:); fill_right];
  
  for a = 1:n_times
    % These Inf values won't go in the result anyway
    aux = min( [ aux, [aux(2:end); -Inf], [-Inf; aux(1:(end-1))] ], [], 2 );
  end
  
  y = aux((1+n_times):(end-n_times));

  y = reshape( y, siz );