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To comment in MATLAB, start a line with the percent sign (%). MATLAB ignores everything after the % on that line. To comment several lines at once, wrap them in %{ and %} on their own lines, or select the lines in the Editor and use the Comment button or its keyboard shortcut. This guide is for researchers and analysts who want clear, shareable analysis scripts.
What comments are used for in research code
MATLAB’s documentation says to add comments to code with the percent symbol, either on a line of its own or at the end of a line of code. In research work, comments do three jobs: they explain why a step exists (for a collaborator or a reviewer), they switch code off temporarily while debugging, and, when placed at the top of a file, they become the help text that MATLAB prints for that program. Well-commented scripts are one small part of reproducible research practices and make code review of research software easier.
Which comment syntax works where
| Syntax | What it does | Rule from the MathWorks documentation |
|---|---|---|
% |
Comments out the rest of the line | Can start a line or follow code on the same line |
%{ ... %} |
Comments out a block of lines | The %{ and %} operators must appear alone on their lines, with no other text on those lines |
... (ellipsis) |
Continues a statement on the next line | Use it instead of % to comment part of a multi-line statement |
%% |
Starts a code section; the text after it is the section title | Section titles are comments that begin with %% |
| Comment block at the top of a file | Becomes the help text shown by help |
For a function, place it directly below the function definition line (or below the arguments block) |
Single-line comments: comment in MATLAB with %
Comment in MATLAB at the start of a line
Type % as the first character, then your text. The whole line is ignored when the script runs.
% Load the raw measurements
data = readmatrix('trial1.csv');MATLAB comments at the end of a line
Place % after a statement to annotate it without disabling it.
threshold = 0.05; % significance level used in all testsBlock comments: comments in MATLAB across many lines
Put %{ on a line by itself, then the lines to disable, then %} on a line by itself.
%{
data = readmatrix('trial2.csv');
summary(data)
%}The documentation states that the block operators must appear alone on their lines. Do not put text, including a note such as %{ old analysis, on the same line as %{ or %}; keep any explanation on a separate % line above the block.
Comment and uncomment with the Editor button or a shortcut
- Open the file in the MATLAB Editor or the Live Editor.
- Select the lines you want to comment.
- In the Code section, click Comment. To reverse it, select the same lines and click Uncomment.
The MathWorks comments page lists keyboard shortcuts for the same actions: on Windows, Ctrl+R comments the selection; on Linux, Ctrl+/ comments and Ctrl+Shift+/ uncomments; on macOS, Command+/ comments and Command+Option+/ uncomments. Sources differ on the Windows uncomment shortcut (one MathWorks Answers reply gives Ctrl+T for the Windows default set), so check your own binding as described below.
If the comment shortcut does nothing
MathWorks Answers advises checking the active binding: go to the Home tab, open Preferences (Environment), then MATLAB > Keyboard > Shortcuts, and search for the action “Comment” to see which shortcut is assigned. You can also select the Windows Default Set there. Another application may be intercepting the key combination, so test it with the other program closed.
Comment out part of a multi-line statement
A % comment runs to the end of its line. The documentation says to use the ellipsis (...) to continue a statement across lines, in place of %, when you want to comment part of a multi-line statement.
Section titles and help text
A line beginning with %% starts a section, and its text is the section title. Comments placed at the start of a program also serve as help text. For a function, that block goes directly below the function definition line. Its first line is the H1 line: the program name plus a brief description, which MATLAB uses in the Files panel, in help, and in lookfor. Running help followed by the program name prints that comment block; comment lines after the help block are ignored by help. For lab scripts that others will reuse, a clear H1 line is the cheapest documentation you can add.
Troubleshooting
- A block comment is not working. Check that
%{and%}are each alone on their line, with nothing else, per the documentation. - The shortcut does nothing. Check Preferences > Keyboard > Shortcuts as above, and close other programs that may capture the key combination.
- Help prints the wrong text. Help text must be the comment block at the start of the program, directly under the function definition line for functions.
Free alternative: GNU Octave
| Tool | Single-line comment character | Source |
|---|---|---|
| MATLAB | % |
MathWorks documentation |
| GNU Octave | # or %; text after it is ignored |
Octave manual, Single-Line Comments |
Because Octave accepts % as well, simple single-line comments written for MATLAB use a character Octave also treats as a comment.
Frequently asked questions
How do you comment in MATLAB?
Start the line with %. Everything after it on that line is ignored. For several lines, use %{ and %} on their own lines or the Editor’s Comment button.
How do you write a block comment in MATLAB?
Put %{ alone on one line, your lines below it, and %} alone on the last line. No other text may share those two lines.
What is the shortcut for comments in MATLAB?
On Windows the documented comment shortcut is Ctrl+R; on Linux it is Ctrl+/ and on macOS Command+/. Confirm the binding in Preferences > Keyboard > Shortcuts.
How do you comment part of a multi-line statement?
Use the ellipsis (...) to continue the statement instead of %, as the documentation describes.
Related reading: MATLAB coding: scripts, functions and a first program, MATLAB code, MATLAB if statements and MATLAB documentation.
Sources
- MathWorks, Comments (MATLAB documentation), read 2026-11-08.
- MathWorks, Add Help for Your Program, read 2026-11-08.
- MathWorks Answers, Unable to use Ctrl+R to comment, read 2026-11-08.
- GNU Octave manual, Single-Line Comments, read 2026-11-08.
