Matlab Quick reference¶
Page last updated on: 2019-10-14
The Matlab Work Environment¶
General Commands¶
Tip
Some commands have links to syntax details and examples.
| Command | Description |
|---|---|
| clc | Clear Command Window |
| clear | Remove items from workspace, freeing up system memory |
| close all | Close all plots |
| doc function | Display documentation page in Help browser |
| help | Help for functions in Command Window |
| ver | Version information for MathWorks products |
| % some comment text | Comment text |
| CTRL+C | Abort the current operation |
| format short | Display 4 decimal places |
| format long | Display 15 decimal places |
| disp('some text') | Print some text |
Defining Variables¶
| Command | Description |
|---|---|
| a = 3 | Define variable a to be 3 |
| x = [1, 2, 3] | Set x to be the row vector [1, 2, 3] |
| x = [1; 2; 3] | Set x to be the column vector [1, 2, 3]T |
| A = [1, 2, 3, 4, 5, 6; 7, 8, 9, 10, 11, 12] |
Set A to be a 2 × 6 matrix |
| x(2) = 7 | Change x from [1, 2, 3] to [1, 7, 3] |
| A(2,1) = 0 | Change A2,1 from 5 to 0 |
Basic Arithmetic¶
| Command | Description |
|---|---|
| 3*4, 7+4, 2-6, 8/3 | multiply, add, subtract and divide |
| 3^7 | Compute 3^7 |
| sqrt(5) | Compute \sqrt{5} |
| log(3) | Compute natural logarithm ln(3) |
| log10(100) | Compute common logarithm (base 10) log(10) |
| abs(-5) | Compute |-5| |
| sin(5*pi/3) | Compute sin(5\pi/3) |
Round numbers¶
| Command | Description |
|---|---|
| floor(-1.5) | -2; Round toward negative infinity |
| ceil(-1.5) | -1; Round toward positive infinity |
| fix(-1.5) | -1; Round toward zero |
| round(-1.5) | -2; Round to nearest decimal or integer |
Matrices and Vectors¶
| Command | Description |
|---|---|
| zeros(12, 5) | Make a 12 × 5 matrix of zeros |
| ones(12, 5) | Make a 12 × 5 matrix of ones |
| eye(5) | Make a 5 × 5 identity matrix |
| eye(12, 5) | Make a 12 × 5 identity matrix |
| linspace(1.4, 6.3, 1004) | Make a vector with 1004 elements evenly spaced between 1.4 and 6.3 |
| logspace(1.4, 6.3, 1004) | Make a vector with 1004 elements where the log of the spacing is evenly increasing between 1.4 and 6.3 |
| 7:15 | Row vector of 7, 8, . . . , 14, 15 |
Operations on Matrices and Vectors¶
| Command | Description |
|---|---|
| 3 * x | Multiply every element of x by 3 |
| x + 2 | Add 2 to every element of x |
| x + y | Element-wise addition of two vectors x and y |
| A * y | Product of a matrix and vector |
| A * B | Product of two matrices |
| A .* B | Element-wise product of two matrices |
| A ^ 3 | Square matrix A to the third power |
| A .^ 3 | Every element of A to the third power |
| cos(A) | Compute the cosine of every element of A |
| abs(A) | Compute the absolute values of every element of A |
| A' | Transpose of A |
| inv(A) | Compute the inverse of A |
| det(A) | Compute the determinant of A |
| eig(A) | Compute the eigenvalues of A |
| size(A) | Get the size of A |
Slicing Matrices and vectors¶
| Command | Description |
|---|---|
| x(2:12) | The 2nd to the 12th elements of x |
| x(2:end) | The 2nd to the last elements of x |
| x(1:3:end) | Every third element of x from the first to last |
| A(5,:) | Get the 5th row of A |
| A(:,5) | Get the 5th column of A |
| A(5, 1:3) | Get the first to third elements in the 5th row |
Constants¶
| Command | Description |
|---|---|
| pi | \pi = 3.141592653589793 |
| NaN | Not a number (i.e. 0/0) |
| Inf | Infinity |
| realmax | Largest positive floating-point number 1.7977x10^{308} |
| realmin | Smallest positive floating-point number 2.2251x10^{−308} |
Loops¶
For loop:
for k = 1:5
disp(k);
end
While loop:
k = 0;
while k < 7
k = k + 1;
end
Logicals¶
a = 10
a == 5 % Test if a is equal to 5
false
a == 10 % Test if a is equal to 10
true
a >= 5 % Test if a is greater than or equal to 5
true
a < 11 % Test if a is less than 11
true
a ~= 4 % Test if a is not equal to 4
true
a > 1 && a ~= 10 % Test if a is greater than 1 AND not equal to 10
false
a > 1 || a ~= 10 % Test if a is greater than 1 OR not equal to 10
true
Conditional Statements¶
if a > 10
disp('Greater than 10');
elseif a == 5
disp('a is 5');
else
disp('Neither condition met');
end
Functions¶
function output = addNumbers(x, y)
output = x + y;
end
addNumbers(10, -5)
5
Plotting¶
| Command | Description |
|---|---|
| plot(x,y) | Plot y versus x (must be the same length) |
| loglog(x,y) | Plot y versus x on a log-log scale (both axes have a logarithmic scale) |
| semilogx(x, y) | Plot y versus x with x on a log scale |
| semilogy(x, y) | Plot y versus x with y on a log scale |
| axis equal | Force the x and y axes to be scaled equally |
| title('A Title') | Add a title to the plot |
| xlabel('x label') | Add a label to the x axis |
| ylabel('y label') | Add a label to the y axis |
| legend('foo', 'bar') | Label 2 curves for the plot |
| grid | Add a grid to the plot |
| hold on | Multiple plots on single figure |
| figure | Start a new plot |
Example:
x = linspace(-3*pi, 3*pi, 1000);
y1 = sin(x);
y2 = cos(x);
plot(x, y1, 'k-'); % Plot sin(x) as a black line
hold on % Now we can add another curve
plot(x, y2, 'r-'); % Plot cos(x) as a red line
% Set the axis limits
axis([-3*pi, 3*pi, -1.5, 1.5])
% Add axis labels
xlabel('x');
ylabel('y');
% Add a title
title('A plot of cos(x) and sin(x)');
% Add a legend
legend('sin(x)', 'cos(x)');
Last update: 2019-10-14