Introduction to Matlab

MATLAB: Script Files

This tutorial introduces creating, running, and modifying MATLAB scripts. You will also practise using loops and conditional statements.

1. What is a script?

A MATLAB script is a file containing a sequence of commands. When you run the script, MATLAB executes these commands in order. Scripts allow you to save, repeat, and modify calculations without retyping commands in the Command Window.

In this tutorial, you will work with plain-text scripts saved with the .m extension.

When naming a script:

  • Start the name with a letter.
  • Use letters, digits, and underscores.
  • Avoid spaces and arithmetic symbols such as + or -.
  • Avoid names of built-in functions, such as plot.m or sin.m.

For example, sine_plot.m is a suitable filename.

Use % to add comments explaining your code. A semicolon ; at the end of a statement suppresses its output in the Command Window; the statement is still executed.

2. Creating and running a script

  1. Select New Script in MATLAB to open the Editor.
  2. Enter the code shown below.
  3. Save the file as sine_plot.m in your current MATLAB folder.
  4. Click Run in the Editor.
% Plot the sine function over the interval [0, 2*pi]
x = 0:pi/100:2*pi;
y = sin(x);

figure;
plot(x, y);
xlim([0 2*pi]);
xlabel('x [rad]');
ylabel('sin(x)');
title('Sine function', 'FontSize', 12);
grid on;

The script defines the values of x, calculates the corresponding values of sin(x), and displays a labelled plot.

You can also run the script by typing its name, without the .m extension, in the Command Window: 

sine_plot

For this method, the file must be in the current folder or in a folder on the MATLAB search path.

Important: Do not include the Command Window prompt >> in a script.

3. Editing a script

Open an existing script in the MATLAB Editor, modify the required commands, save the file, and run it again.

To change the previous example from a sine plot to a cosine plot:

  • Replace y = sin(x); with y = cos(x);.
  • Change the vertical-axis label to cos(x).
  • Change the title to Cosine function.
  • Save the modified script as cosine_plot.m to preserve the original example.

Remember to update labels and comments whenever you change the calculations.

Example: modifying matrix calculations

Scripts can also be used to repeat matrix calculations with different input data: 

% Define a scalar and a 3-by-3 matrix
a1 = 5.5;
B = [1 4 17; 20 0 5; 4 9 11];

% Calculate a1 multiplied by the inverse of B
C = a1 * B^-1

Here, B^-1 denotes the matrix inverse, not the reciprocal of each element. The matrix must be nonsingular. The result C is displayed because the last statement does not end with a semicolon.

Replace the definition of B with:

B = [1 4 22; 20 23 5; 54 9 11];

Save and rerun the script. Compare the new matrix C with the previous result.

Numerical practice: When solving a linear system B*u = f, use u = B\f rather than explicitly calculating the inverse.

4. Repeating calculations: the for loop

A for loop repeats a set of commands for successive values of an index. The following example calculates the first ten positive integer powers of 2: 

% Allocate space for ten results
A = zeros(1, 10);

% Calculate successive powers of 2
for n = 1:10
    A(n) = 2^n;
end

disp(A);

The index n takes the values 1 through 10. During each iteration, the result is stored in the corresponding element of A. The keyword end closes the loop.

Expected output:

2   4   8   16   32   64   128   256   512   1024

5. Selecting calculations: the if–else statement

An if–else statement selects which commands to execute depending on whether a condition is true.

The following script evaluates a function using one expression for x <= 20 and another for x > 20: 

x = 1:50;
y = zeros(size(x));

for k = 1:length(x)
    if x(k) <= 20
        y(k) = 2*x(k) + 5;
    else
        y(k) = -x(k) + 65;
    end
end

figure;
plot(x, y, 'LineWidth', 1.5);
xlabel('x');
ylabel('y');
title('Piecewise-defined function');
grid on;

The first end closes the conditional statement; the second closes the loop. Indentation helps make this structure clear. Here, k is the array index, while x(k) is the corresponding argument of the function.

6. Practice tasks

  1. Create and run sine_plot.m.
  2. Save a modified version as cosine_plot.m and update the labels and title.
  3. Modify the loop example to calculate the first ten positive integer powers of 3.
  4. Run the piecewise-function example and check the calculated values at x = 20 and x = 21.
  5. Explain the purpose of %, ;, for, if, else, and end.
Before you finish: Make sure that your scripts run successfully, contain appropriate comments, and produce results that you can explain.

6. Formatting and exporting plots

A figure prepared for a report should have readable axis labels, appropriate axis limits, and sufficient image resolution. The following examples show how to control these properties in a script.

6.1. Adding axis labels and a title

Run this example to create a plot. Use xlabel and ylabel to describe the axes, including units where appropriate. Use title to add a title. 

x = 0:pi/100:2*pi;
y = sin(x);

figure;
plot(x, y, 'b-', 'LineWidth', 1.5);

xlabel('x [rad]', 'FontSize', 12);
ylabel('sin(x) [-]', 'FontSize', 12);
title('Sine function', 'FontSize', 14);

set(gca, 'FontName', 'Arial', 'FontSize', 12);
grid on;
box on;

gcf refers to the current figure, while gca refers to the current axes. A figure can contain several axes, for example when using subplot.

6.2. Changing axis limits

Set the horizontal and vertical ranges separately using xlim and ylim: 

xlim([0 2*pi]);
ylim([-1.2 1.2]);

Alternatively, set both ranges with one command. The order is [xmin xmax ymin ymax]: 

axis([0 2*pi -1.2 1.2]);

Narrower limits display a selected part of the data; wider limits add space around the curve. For example: 

% Display only part of the curve
xlim([pi/2 3*pi/2]);

% Extend the displayed range beyond the data
xlim([-0.5 2*pi+0.5]);
ylim([-1.5 1.5]);

These commands change the displayed region without modifying or deleting the underlying data.

The following commands are alternatives for automatic adjustment. Run the one that gives the required result: 

axis tight;   % Fit the axis limits to the data range
axis padded;  % Add a small margin around the data
axis auto;    % Restore automatic axis limits

Tick positions can also be specified explicitly:

set(gca, 'YTick', -1:0.5:1);

6.3. Changing the figure size and plotting area

The figure size and the axis limits are independent. Resizing the figure changes its layout, not the range of data. For a separate figure window, specify its position and size in pixels: 

set(gcf, 'WindowStyle', 'normal');
set(gcf, 'Units', 'pixels');
set(gcf, 'Position', [100 100 900 450]);

The four values are [left bottom width height]. In this example, the figure is 900 pixels wide and 450 pixels high. These on-screen dimensions do not necessarily equal the dimensions of the exported PNG.

To adjust the plotting area within the figure, change the axes position: 

set(gca, 'Units', 'normalized');
set(gca, 'Position', [0.12 0.18 0.83 0.72]);

Here, [left bottom width height] is expressed as fractions of the parent container dimensions. Increasing the width or height enlarges the plotting area and reduces the space available for labels. Leave sufficient room for axis labels, tick labels, and the title.

6.4. Saving a PNG file and setting its resolution

In MATLAB R2020a or later, use exportgraphics to export the current axes, including their labels and title: 

exportgraphics(gca, 'sine_plot.png', ...
    'Resolution', 300, 'BackgroundColor', 'white');

The file is saved in the current folder unless a different path is specified. The value 300 sets the resolution to 300 dots per inch (DPI). At the same physical size, increasing DPI increases the number of image pixels and usually the file size. It does not improve the accuracy of the plotted data.

An alternative, also available in older MATLAB versions, is print. This exports the figure: 

set(gcf, 'Color', 'white');
set(gcf, 'PaperPositionMode', 'auto');
print(gcf, 'sine_plot.png', '-dpng', '-r300');
  • -dpng selects the PNG format.
  • -r300 selects 300 DPI; use -r150 for 150 DPI.
  • PaperPositionMode set to auto bases the printed size on the figure size.

To control the physical output size explicitly with print, set the paper position in inches: 

set(gcf, 'PaperUnits', 'inches');
set(gcf, 'PaperPosition', [0 0 6 3]);
set(gcf, 'PaperPositionMode', 'manual');

print(gcf, 'sine_plot_1800x900.png', '-dpng', '-r300');

A 6-by-3-inch image exported at 300 DPI has dimensions of 1800 by 900 pixels.

6.5. Cropping or extending the outer margins

Cropping the outer margins removes unnecessary blank space around the plot. This is different from changing the axis limits. By default, exportgraphics exports a tightly cropped plot while retaining its labels and title.

In locally installed MATLAB R2025a or later, the Padding option provides additional control. The following examples are alternatives: 

% Crop unnecessary outer whitespace
exportgraphics(gca, 'plot_tight.png', ...
    'Resolution', 300, 'Padding', 'tight');

% Add a 20-pixel outer margin
exportgraphics(gca, 'plot_margin.png', ...
    'Resolution', 300, 'Units', 'pixels', 'Padding', 20);

% Preserve the relative margins shown in the figure
exportgraphics(gca, 'plot_figure_margins.png', ...
    'Resolution', 300, 'Padding', 'figure');
Check the exported file: Open the PNG and confirm that all labels are visible, the text is readable at the intended display size, and the selected axis limits show the relevant results.

6.6. Complete example

This script creates a labelled plot, sets its dimensions and axis limits, and saves it as a PNG file at 300 DPI. It requires MATLAB R2020a or later. 

% Input data
x = 0:pi/100:2*pi;
y = sin(x);

% Create a figure and axes
fig = figure('Color', 'white', 'WindowStyle', 'normal');
set(fig, 'Units', 'pixels', 'Position', [100 100 900 450]);
ax = axes('Parent', fig);

% Draw and format the curve
plot(ax, x, y, 'b-', 'LineWidth', 1.5);
xlabel(ax, 'x [rad]', 'FontSize', 12);
ylabel(ax, 'sin(x) [-]', 'FontSize', 12);
title(ax, 'Sine function', 'FontSize', 14);

set(ax, 'FontName', 'Arial', 'FontSize', 12);
set(ax, 'Units', 'normalized', ...
    'Position', [0.12 0.18 0.83 0.72]);

xlim(ax, [0 2*pi]);
ylim(ax, [-1.2 1.2]);
grid(ax, 'on');
box(ax, 'on');

% Export the axes, labels, and title
exportgraphics(ax, 'sine_plot.png', ...
    'Resolution', 300, 'BackgroundColor', 'white');

Practice: Export the same plot at 150 and 300 DPI. Compare the pixel dimensions, file sizes, and appearance when enlarged. Then change the horizontal limits to [0 pi] and save the result under a different name.

Ostatnia modyfikacja: środa, 30 wrzesień 2026, 14:45