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I'm trying to plot some annotations to go along with my step function graphs. I currently have these graphs, and I've been trying to figure out how to draw horizontal arrows that point towards vertical lines. I will also need labeled, vertical lines that are pointing towards horizontal lines.

I have attached an image that shows (in red) what I mean. I've tried the annotation() function, but it's truly a pain to get the arrows where I want them to be. If anyone wouldn't mind explaining how to use that function, or alternative methods for what I'm trying to achieve, that would be amazing!

Matlab Plot with arrows I would like to achieve.

EDIT: Is there a way to edit the Quiver arrowhead size?

enter image description here

Cory
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1 Answers1

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Using Quiver in a 2D Subplot

Not quite sure if this is any better or simpler but I used the quiver() function to plot the lines shown below. The quiver() function takes in a few inputs in this case. In the full script below I used twice the amount of quiver() calls to plot overlapping arrows to create a double headed arrow.

Quiver Arrow Annotations

Function Call:

quiver(Start_Point(1),Start_Point(2),X_Displacement,Y_Displacement,0);

• Start_Point → equal to [x y] (x-coordinate y-coordinate)
• Start_Point(1) → The x-coordinate of the arrow's start
• Start_Point(2) → The y-coordinate of the arrow's start
• X_Displacement → The horizontal distance from the start of the array
• Y_Displacement → The vertical distance from the start of the array

Setting the Maximum Size of the Arrow Head:

The maximum size of the arrow head can be set by using the 'MaxHeadSize' property.

clf;
Start_Point(1) = 0;
Start_Point(2) = 0;
X_Displacement = 0; Y_Displacement = 10;
Magnitude = sqrt(X_Displacement.^2 + Y_Displacement.^2);

quiver(Start_Point(1),Start_Point(2),X_Displacement,Y_Displacement,0,'Color','r','MaxHeadSize',1/Magnitude);
hold on 

Start_Point(1) = 0;
Start_Point(2) = 0;
X_Displacement = 100; Y_Displacement = 0;
Magnitude = sqrt(X_Displacement.^2 + Y_Displacement.^2);
quiver(Start_Point(1),Start_Point(2),X_Displacement,Y_Displacement,0,'Color','r','MaxHeadSize',1/Magnitude);
MichaelTr7
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    Perfect! Thanks so much for the help! – Cory Jan 27 '21 at 17:35
  • @Cory No problem, happy to help. – MichaelTr7 Jan 27 '21 at 23:28
  • I was able to get the arrows to work out, but for some of my functions the arrowheads are huge. Is there a way to make them a certain size? I edited the initial post with an example. – Cory Jan 29 '21 at 05:04
  • Using the `MaxHeadSize` property may help. I added a script in my answer that tries to normalize this according to the magnitude/length of the arrow since the arrow head is proportional to its length. – MichaelTr7 Jan 29 '21 at 05:16