How to draw only a part of a known curve?

I have made this

The blue plot, is a curve defined like this:

curve=[xco0 xco1 xco2 xco3 xco4 xco5 xco6 xco7 xco8;yco0 yco1 yco2 yco3 yco4 yco5 yco6 yco7 yco8];

Which each x and y components, are its known coordinates. Each one has a lot of values in it.

I also have pointA and pointB, which are points of the curve which coordinates are known:

pointA=[ax;ay];
pointB=[bx;by];

The issue here is that I would like to draw only the part of the curve that is between those two points, or to colour the curve as white the rest of the curve that is not between pointA and pointB, which is the same thing in fact.

How can I do that?

Answer 1

[Fangjun Jiang]

x=1:0.1:10;
y=sin(x);
index=and(x>3, x<6);
plot(x(index),y(index))

[Adam Danz]

Alternatively, replace unwanted values with NaN.

% Assuming 'curve' is a 2xn matrix defining [x;y] values
curve(:,~index) = NaN; 
plot(curve(1,:), curve(2,:))

[ErikJon Pérez Mardaras]

What am I doing wrong?

I have put this as Fangjun Jiang said and it doesn't work

x=xco0:xco8;
index=and(x>ax, x<bx);
plot(x(index),curve(index));

[Adam Danz]

" it doesn't work" does not describe what the problem is.

What are the size and shape of your variables?

Are you getting an error message?

Why doesn't it work?

[ErikJon Pérez Mardaras]

• As I said in the question, the curve named curve is made-up of a series of coordinates in a matrix:

    curve=[xco0 xco1 xco2 xco3 xco4 xco5 xco6 xco7 xco8;yco0 yco1 yco2 yco3 yco4 yco5 yco6 yco7 yco8];

Each element (xco0, xc1, yc0...etc) has 100 elements inside, so the matrix curve is a 2x900 dimension matrix. (2rows and 900 columns)

• No, any error message is shown
• I have put that code that I say above in the previous message:

x=xco0:xco8;
index=and(x>ax, x<bx);
plot(x(index),curve(index));

and it doesn't draw me anything, that's why I say that doesn't work.

[Fangjun Jiang]

%%
curve=[0:0.1:6;sin(0:0.1:6)];
pointA=[2;sin(2)];
pointB=[5;sin(5)];

%%
figure(1);
plot(curve(1,:),curve(2,:));

%%
index=and(curve(1,:)>=pointA(1),curve(1,:)<=pointB(1));
figure(2);
plot(curve(1,index),curve(2,index));

[ErikJon Pérez Mardaras]

Thanks for your reply. But in that code you say basically, how to plot the curve with the condition that the X coordinates of the curve have to be between the X coordinate of point A and the Y coordinate of point B.

But I need another condition. I also need the condition that the Y coordinates of the curve have to be between the Y coordinates of point A and Y coordinates of point B, which code, if I`m not wrong is:

indey=and(curve(2,:)>=pointA(2),curve(2,:)<=pointB(2));

The question is, how can I plot the curve with both conditions index and indey?

As you said, plotting with one condition only (index) is made like that:

plot(curve(1,index),curve(2,index));

But when you have those two conditions? How do you plot that?

[Fangjun Jiang]

do this further

index=and(index, indey);

[ErikJon Pérez Mardaras]

Actually, I have tried that more and it doesn`t work for certain cases.

For instance, let`s have the following curve and the following points A and B

Okay, now I woul like to draw only the part of the curve that is between pointA and pointB.

But, according to your answer, if I code what is putted there, matlab will not draw me what I want. In order, it will draw me all parts of the curve that it is between the dash lines. I mean, that part of the curve that is between purple dash lines and orange dash lineas, I mean, that:

And that is not what I am looking for. What I am looking for is to draw this:

Is there any way of doing it?

[Fangjun Jiang]

In this case, index=and(y>Ya, y<Yb) is sufficient. It is due to the fact that x values exceed Xb and then comes back. Same thing could happen to y values. It is a math problem, not a MATLAB problem. You need to consider different and all the cases of your curves.

Just like your figure illustrated, index1=and(y>Ya,y<Yb) gives you the area between two purple dash lines. index2=and(x>Xa,x<Xb) gives you the area between two orange dash lines. index=and(index1, index2) gives you the rectangel area between those four dash lines.

[ErikJon Pérez Mardaras]

Thanks for your reply.

But just because of that, I am looking for a general way of doing it, not a particular way that works only for a particular curve. Is there any?