Shade the encircled area

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Muhammad Sanwal
Muhammad Sanwal on 29 Aug 2020
Commented: Star Strider on 2 Sep 2020
Hi. Can anyone please tell me how to shade the encircled area(in red)?
The graph is as follows
And the code is as follows
tx1=-7:0.1:-1;
tx2=-1:0.1:0.5;
tx3=0.5:0.1:3;
tx4=3:0.1:7;
tx=[tx1 tx2 tx3 tx4];
x1=zeros(size(tx1));
x2=0.6.*ones(size(tx2));
x3=0.3.*ones(size(tx3));
x4=zeros(size(tx4));
x=[x1 x2 x3 x4];
th1=-7:0.1:0;
th2=0:0.1:7;
h1=zeros(size(th1));
h2=ones(size(th2));
h3=[h1 h2];
th=[th1 th2];
h4=exp(-th);
h=h3.*h4;
t=0;
plot(tx,x,-th+t,h,'-','linewidth',2)
ylim([-0.1 1.1])
legend('x(\tau)','h(t-\tau)')
grid

Accepted Answer

Star Strider
Star Strider on 30 Aug 2020
After the original code in your Question (not your subsequent Comment), add these lines:
hold on
Ltx = (tx >= -1) & (tx <= 0);
Ltht = (-th+t >= -1) & (-th+t <= 0);
xh = min([x(Ltx); h(Ltht)]);
patch([tx(Ltx) flip(tx(Ltx))], [zeros(size(xh)) xh], 'g')
hold off
to get this plot:
.
  9 Comments
Muhammad Sanwal
Muhammad Sanwal on 2 Sep 2020
Thank you very much!
Star Strider
Star Strider on 2 Sep 2020
As always, my pleasure!

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More Answers (3)

the cyclist
the cyclist on 30 Aug 2020
Combining your new code that aligns the values of t (but not using your attempt at creating the patch), and the same basic idea of Star Strider and Image Analyst, this code accurately aligns the patch as I believe you want. But, as Star Strider says, you decide.
t1=-7:0.1:-1;
t2=-1:0.1:0;
t3=0:0.1:0.5;
t4=0.5:0.1:3;
t5=3:0.1:7;
t=[t1 t2 t3 t4 t5];
x1=zeros(size(t1));
x2=0.6.*ones(size(t2));
x3=0.6.*ones(size(t3));
x4=0.3.*ones(size(t4));
x5=zeros(size(t5));
x=[x1 x2 x3 x4 x5];
h1=zeros(size(t1));
h2=zeros(size(t2));
h3=ones(size(t3));
h4=ones(size(t4));
h5=ones(size(t5));
h6=[h1 h2 h3 h4 h5];
h7=exp(-t);
h=h6.*h7;
figure
hold on
plot(t,x,-t,h,'-','linewidth',2)
ylim([-0.1 1.1])
legend('x(\tau)','h(t-\tau)')
grid
lightGreen = [0.85, 1, 0.85];
xh = min([x; flip(h)]);
plot(t,xh)
patch([flip(t) t], [zeros(size(t)) xh], lightGreen)
  2 Comments
Muhammad Sanwal
Muhammad Sanwal on 30 Aug 2020
both methods work. thanks!
the cyclist
the cyclist on 30 Aug 2020
Glad it worked out. Be aware that the two solutions cover slightly different areas, and this is more evident with the relative large step size (0.1) you are using.
If you use something smaller (e.g. 0.01), both solutions will more sharply align with your lines, visually.

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Bruno Luong
Bruno Luong on 30 Aug 2020
Edited: Bruno Luong on 30 Aug 2020
Use polyshape and let polyshape do the work. Replace plot(P1, ...) with normal plot if you don't like the artefact on x-axis.
t1=-7:0.1:-1;
t2=-1:0.1:0;
t3=0:0.1:0.5;
t4=0.5:0.1:3;
t5=3:0.1:7;
t=[t1 t2 t3 t4 t5];
x1=zeros(size(t1));
x2=0.6.*ones(size(t2));
x3=0.6.*ones(size(t3));
x4=0.3.*ones(size(t4));
x5=zeros(size(t5));
x=[x1 x2 x3 x4 x5];
h1=zeros(size(t1));
h2=zeros(size(t2));
h3=ones(size(t3));
h4=ones(size(t4));
h5=ones(size(t5));
h6=[h1 h2 h3 h4 h5];
h7=exp(-t);
h=h6.*h7;
warning('off','MATLAB:polyshape:repairedBySimplify');
P1=polyshape(t,x);
P2=polyshape(-t,h);
close all
figure
hold on
plot(P2,'facecolor','none','edgecolor','r','linewidth',1)
plot(P1,'facecolor','none','edgecolor','b','linewidth',1)
plot(intersect(P1,P2), 'Facecolor', [0.5, 1, 0.5],'linestyle','none');
ylim([-0.1 1.1])
legend('h(t-\tau)','x(\tau)','whatever')
grid
  2 Comments
Bruno Luong
Bruno Luong on 31 Aug 2020
Edited: Bruno Luong on 31 Aug 2020
Shift annimation:
t1=-7:0.1:-1;
t2=-1:0.1:0;
t3=0:0.1:0.5;
t4=0.5:0.1:3;
t5=3:0.1:7;
t=[t1 t2 t3 t4 t5];
x1=zeros(size(t1));
x2=0.6.*ones(size(t2));
x3=0.6.*ones(size(t3));
x4=0.3.*ones(size(t4));
x5=zeros(size(t5));
x=[x1 x2 x3 x4 x5];
h1=zeros(size(t1));
h2=zeros(size(t2));
h3=ones(size(t3));
h4=ones(size(t4));
h5=ones(size(t5));
h6=[h1 h2 h3 h4 h5];
h7=exp(-t);
h=h6.*h7;
warning('off','MATLAB:polyshape:repairedBySimplify');
close all
figure
for tau=0:0.1:4
cla
hold on
t1 = t;
t2 = tau-t;
P1=polyshape(t1,x);
P2=polyshape(t2,h);
plot(t1,x,'color','r','linewidth',1)
plot(t2,h,'color','b','linewidth',1)
plot(intersect(P1,P2), 'Facecolor', [0.5, 1, 0.5],'linestyle','none');
xlim([-6 12]);
ylim([-0.1 1.1])
legend('h(t-\tau)','x(\tau)','whatever')
grid on
drawnow
end
Muhammad Sanwal
Muhammad Sanwal on 2 Sep 2020
Yes, this code works too. Thankyou!

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Image Analyst
Image Analyst on 29 Aug 2020
  2 Comments
the cyclist
the cyclist on 29 Aug 2020
@muhammad:
Note that the solution that @ImageAnalyst posted makes this statement:
% Assume y1 and y2 have the same number of elements located at the same x values.
Your curves do not obey this assumption, which makes your problem significantly more difficult (I think).
If you can define data in a way that they use the same t (number of elements and same values), this will be an easier task.
Next best would be using at least the same number of elements (if not at the same values).
Muhammad Sanwal
Muhammad Sanwal on 30 Aug 2020
I made my vector t of the same length, but the graph I get is as follows
Please help me make changes to the program so that I can get the original encircled area (in red), as mentioned in my question.
The code is as follows
t1=-7:0.1:-1;
t2=-1:0.1:0;
t3=0:0.1:0.5;
t4=0.5:0.1:3;
t5=3:0.1:7;
t=[t1 t2 t3 t4 t5];
x1=zeros(size(t1));
x2=0.6.*ones(size(t2));
x3=0.6.*ones(size(t3));
x4=0.3.*ones(size(t4));
x5=zeros(size(t5));
x=[x1 x2 x3 x4 x5];
h1=zeros(size(t1));
h2=zeros(size(t2));
h3=ones(size(t3));
h4=ones(size(t4));
h5=ones(size(t5));
h6=[h1 h2 h3 h4 h5];
h7=exp(-t);
h=h6.*h7;
plot(t,x,-t,h,'-','linewidth',2)
ylim([-0.1 1.1])
legend('x(\tau)','h(t-\tau)')
grid
% Shade the area between in light green using the patch() function.
lightGreen = [0.85, 1, 0.85];
% Create the boundaries of the upper points and the lower points.
% Assume x and h have the same number of elements located at the same x values.
upperBoundary = max(x, h);
lowerBoundary = min(x, h);
% Now do the actual display of the shaded region.
patch([t fliplr(t)], [upperBoundary fliplr(lowerBoundary)], lightGreen);
% Plot x and h AFTER the patch so the patch does not cover any of those curves.
hold on;
plot(t, x, 'r-', 'LineWidth', 2); % Plot curve 1 in red.
plot(t, h, 'b-', 'LineWidth', 2); % Plot curve 2 in blue.
legend('Patch', 'y1', 'y2');
% Maximize the figure window
g = gcf; % Setting the WindowState on gcf directly doesn't work for some reason.
g.WindowState = 'maximized'

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