If you want to manually decide where the partition line is, then this is more or less how you would go about recreating your Excel chart in Matlab, obviously using real data:
% Randomly generated data
x = 1:30;
y = 0.5*x;
y(1:10) = y(1:10).*rand(1,10);
y(11:20) = y(11:20)+4*rand(1,10);
y(21:30) = y(21:30)+8*rand(1,10);
% partition lines data
x1 = [min(x) max(x)]; % x-range for the partition lines
y1 = [4 4]; % dashed black line
y2 = [15 15]; % dashed red line
% main plot
figure
p(1) = plot(x,y);
hold on
p(2) = plot(x1,y1);
p(3) = plot(x1,y2);
title('Chart title')
xlabel('x-axis data')
ylabel('y-axis data')
legend({'Main data' 'partition A' 'partition B'},...
'Location','best')
% set the properties of the lines
% p(1) - main data
set(p(1),...
'LineStyle' ,'-',...
'LineWidth' ,0.5,...
'Color' , [0 0 0],...
'Marker' , '.',...
'MarkerSize' , 12,...
'MarkerFaceColor',[0 0 1],...
'MarkerEdgeColor',[0 0 1]);
% p(2) and p(3) - partition lines COMMON settigs
set([p(2), p(3)],...
'LineStyle','--',...
'LineWidth',0.5);
% p(2) - color
set(p(2),...
'Color', [0 0 0]);
set(p(3),...
'Color', [1 0 0]);
The output:
