% Create sample data.
y = randi(160, 1, 40); % Array of random numbers
x = 1 : length(y);
% Plot everything with blue spots and blue lines between them.
plot(x, y, 'bo-', 'LineWidth', 2, 'MarkerSize', 7);
grid on;
% Now define a threshold.
threshold = 100;
moreThanThreshold = y > 100; % Logical indexes.
% Extract those over the threshold into new arrays.
over_x = x(moreThanThreshold);
over_y = y(moreThanThreshold);
% Now plot those over 100 with red stars over the first set of points.
hold on; % Important so you don't blow the first plot away.
plot(over_x, over_y, 'r*', 'LineWidth', 2, 'MarkerSize', 13);
