To annotate MATLAB graphs with text arrows (text annotations connected to an arrow), you can use the annotation function or the textarrow function.

To annotate MATLAB graphs with text arrows (text annotations connected to an arrow), you can use the annotation function or the textarrow function. Here’s a step-by-step guide:

1. Basic Text Arrow Using `annotation`

The annotation function allows you to add arrows with text labels.
Syntax:

annotation('textarrow', [x_start, x_end], [y_start, y_end], 'String', 'Your Text');

Example:

% Create a plot
x = 0:0.1:2*pi;
y = sin(x);
plot(x, y);
hold on;

% Add a text arrow pointing to a peak
annotation('textarrow', [0.5, 0.6], [0.7, 0.8], ...
    'String', 'Peak Here', ...
    'FontSize', 10, ...
    'Color', 'red', ...
    'TextColor', 'black');

[x_start, x_end] and [y_start, y_end] are normalized coordinates (relative to the figure window, from 0 to 1).
Adjust positions by trial and error or use ginput to interactively select coordinates.

2. Using `textarrow` (Object-Oriented Approach)

For more control over arrow properties, use textarrow:

% Create a text arrow in data coordinates (not normalized)
ta = textarrow([x_start, x_end], [y_start, y_end], 'Your Text');
set(ta, 'Color', 'blue', 'LineWidth', 1.5, 'HeadLength', 10);

Example:

plot(x, y);
hold on;
ta = textarrow([pi/2, pi/2], [1, 0.8], 'Max Value');
set(ta, 'FontSize', 12, 'HorizontalAlignment', 'center');

3. Positioning in Data Coordinates

To place the arrow using data coordinates (e.g., matching the plot’s x/y axis):

Convert data coordinates to normalized figure coordinates using dsxy2figxy (custom function below).
Use the normalized coordinates in annotation.

Custom Helper Function:

function [x_norm, y_norm] = dsxy2figxy(ax, x_data, y_data)
% Convert data coordinates to normalized figure coordinates
pos = ax.Position;
x_norm = (x_data - ax.XLim(1)) / diff(ax.XLim) * pos(3) + pos(1);
y_norm = (y_data - ax.YLim(1)) / diff(ax.YLim) * pos(4) + pos(2);
end

Usage:

ax = gca;
[x_start_norm, y_start_norm] = dsxy2figxy(ax, 3, 0.5); % Data point (3, 0.5)
[x_end_norm, y_end_norm] = dsxy2figxy(ax, 4, 0.8);    % Arrow tip at (4, 0.8)
annotation('textarrow', [x_start_norm, x_end_norm], [y_end_norm, y_start_norm], ...
    'String', 'Important Point');

4. Customizing the Arrow

Modify properties like color, head size, and text alignment:

annotation('textarrow', [0.3, 0.4], [0.5, 0.6], ...
    'String', 'Note This!', ...
    'FontSize', 12, ...
    'Color', 'green', ...
    'HeadWidth', 15, ...       % Arrowhead width
    'HeadLength', 20, ...      % Arrowhead length
    'TextEdgeColor', 'none', ... % Remove text box border
    'TextBackgroundColor', [1 1 1 0.5]); % Semi-transparent white background

5. Using `gtext` for Interactive Placement

For manual placement during runtime:

gtext('Drag to Position', 'FontWeight', 'bold', 'Color', 'magenta');

A crosshair will appear; click to place the text arrow.

Key Tips

Normalized Coordinates: [0, 1] for the entire figure window (bottom-left to top-right).
Data Coordinates: Use textarrow or convert data points to normalized units.
Alignment: Use HorizontalAlignment and VerticalAlignment to adjust text position relative to the arrow.
Overlap Issues: Set TextBackgroundColor to make text readable.

Example Workflow

% Plot data
x = 1:10;
y = rand(1,10);
plot(x, y, 'o-');

% Add text arrow pointing to a specific data point
annotation('textarrow', [0.5, 0.55], [0.6, 0.7], ...
    'String', 'Outlier', ...
    'Color', 'red', ...
    'FontSize', 10);

% Add another arrow using data coordinates
ax = gca;
[x1, y1] = dsxy2figxy(ax, 8, y(8));  % Data point (8, y(8))
[x2, y2] = dsxy2figxy(ax, 7.5, y(8)+0.1);
annotation('textarrow', [x1, x2], [y1, y2], ...
    'String', 'High Value', ...
    'HeadWidth', 20);

Troubleshooting

Arrow Not Visible: Check if coordinates are outside the figure bounds.
Text Overlaps Plot: Adjust the arrow position or use a semi-transparent background.

For more details, see MATLAB’s documentation on annotation or textarrow.

1. Basic Text Arrow Using annotation

2. Using textarrow (Object-Oriented Approach)