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Chapter 1
Introduction to MATLAB
1.1 Software Philosophy
- Matrix-based numeric computation
- MATrix LABoratory
- built-in support for standard matrix and vector operations
- High-level programming language
- Programming data type specification not required
- No pointers
- Interpreted language - commands are executed interactively
- Superb graphics provide excellent data visualization
- Toolboxes provide application specific functionality
- Recent support for structured programming
1.2 Example Uses of Matlab
- A few examples of how MATLAB is used in industry
- Signal generation
- Modeling and analysis of Digital Signal Processing systems
- Communications systems
- Complex mathematical computation
- Control Systems Modeling
- RADAR/SONAR simulation
- Financial Engineering
- many, many others
1.3 The MATLAB Windows
- Three Main Windows (see Figure 1.1):
Main Window – Opens when you start Matlab
- Divided into three panes: Command Most important area on screen: type commands at the command prompt (>> ) Workspace shows currently defined variables; may also be used to display contents of working directory. History Recently entered commands. Editor Allows you to edit Matlab programs.
- Opened via File | New | M-file, or
- via File | Open for editing existing files. Figure Shows plots.
- New windows are opened with the figure command
- The result of the plot or similar commands appear in the active Figure window.
1.4 Getting Help
help Online help for MATLAB functions and M-files
- Accessed via help command
- To get help on function named func, you would type help func,
- Try help help or help plot or help :
doc Starts the Matlab documentation viewer in a separate window.
- Invoked by typing doc or by choosing Help |MATLAB Help from the menu bar.
- Online, in-depth reference manual to all of Matlabs features and functions.
- Contains many demos.
lookfor Searches the help documentation for the keyword provided
- Try lookfor inverse to find all functions that perform some form of inverse operation.
- Warning: this may take a while and find many more functions tham you expected.
1.5 Interacting with the File System
- The following commands allow you to change directories, view directory listings, or display the contents of files with the command window.
cd change working directory
- The command cd directory where directory is the name of a directory, changes the working directory to the indicated directory
- Important: For Matlab to be able to find your own programs and functions, they must be stored in the working directory.
- Changing directories is more conveniently accomplished via the file-system browser near the top of the main window.
- The command cd by itself prints the name of the current directory.
- So does the command pwd. dir list contents of working directory
- The command dir lists the names of the files in the working directory.
- So does the command ls.
- dir may be invoked with the name of a directory, to list the contents of that directory.
- This functionality is also available by selcting the current Directory view in the top left pane of the main window. type display the contents of a file.
- The command type filename displays the contents of the file filename.
- For large files, it may be useful to use the command more on.
- This displays the contents of the file one screen at a time; use the space bar to advance to the next page and the Enter-key to advance by one line. Press ’q’ to stop paging and return to the command prompt.
- Use more off to turn of paging.
- Alternatively, consider examining files in the editor.
1.6 Quit
- quit -terminates MATLAB session
- The command window and all other windows will disappear at the execution of this command.
- No example. (Class isn’t over yet.)
- Beware! Using quit will not save the current workspace.
- Limitation: You cannot put a diary into the files named “off” or “on”.
- Examples:
diary Test X = 44 Y = [4; 5; 6] diary off dir % Test1 is now in your working subdirectory - notice that there % is no file name extension.
- If you open the file Test1 in the editor, you should see:
X = 44
X =
Y = [4; 5; 6]
Y =
diary off
- Now close Test1 in the editor and go back to the command window. Type:
diary Test
>> A = 15:-2:
diary off
- This will append the above commands and resulting output to the end of file Test1.
- The contents of test1 will be:
X = 44
X =
Y = [4; 5; 6]
Y =
diary off
A = 15:-2:
A =
diary off
1.9 Variables
- MATLAB does not require any type declarations or dimension state- ments.
- When a new variable name is encountered, MATLAB automatically creates the variable and allocates the appropriate amount of storage.
1.11 who and whos
- The command who lists all currently used variables.
- The command whos provides additional information about variables, including - their sizes, and - whether they are complex valued.
1.12 The semicolon
- In MATLAB, the semicolon ; serves multiple important purposes.
- The semicolon is used to mark the end rows in vectors or matrices (see below).
- The semicolon can also be used to separate statements on the same line such as:
Num_of_Students=50; Num_of_Teachers=1; - Perhaps most importantly, it is used to suppress displaying the contents of a variable. - This is extremely useful if the variable stores a long vector or a large matrix. - Example: Num_of_Students= will cause Num_of_Students =
50 to be displayed.
- In contrast Num_of_Students=50; creates no output; the value 50 is still stored in the variable named Num of Students.
1.13 Vectors and Matrices
- MATLAB uses vectors and matrices as their primary type of variables.
- Scalars are simply special cases of matrices (of size 1 × 1).
Column Vectors: are m×1 matrices, i.e., they consist of m rows and 1 column. Row Vectors: are 1 × m matrices, i.e., they consist of 1 row and m columns. Matrices: are two-dimensional rectangular array of real or complex numbers.
- Matrices has hundreds of built-in functions to operate on matrices and vectors.
- This includes all functions you learned about in linear algebra, includ- ing dot products, determinants, matrix inverses, etc.
1.14 Storing values in vectors or matrices
- There are many ways to store values in a matrix or vector, including
Using square brackets: – elements of a matrix are specified di- rectly; for example
v = [2 4 7] produces a row vector with 3 elements: v =
- Instead of spaces, commas (,) may be used to separate ele- ments.
v=[2, 4, 7] yields the exact same result.
- Be careful with expressions like
[1+2 2-2 3] and
Used frequently to pre-allocate storage for large arrays; more efficient that incremental allocation of storage. wavread You may have seen yy=wavread(fileanme) for reading in the samples from the soundclip stored in file filename. Many other functions: Try magic(5), hadamard(4), eye(5), rand(4), or many others. See also help elmat.
Via the colon (:) operator: The colon operator is one of the most useful operators in MATLAB.
- Here we focus on creating vectors with equally spaced ele- ments.
- The colon operator is also extremely useful for refering to specific elements of a vector or matrix (see below.)
- The following creates a vector of evenly spaced elements, start- ing at 1 , ending at 2 , the difference between consecutive ele- ments is 0. xx = 1:0.1:
xx =
- The middle element (i.e., the increment) may be omitted; then the default increment of 1 is used: yy = 1:
yy =
- A very frequently used “idiom” in MATLAB is: fs = 8000; % number of samples per second tt = 0:1/fs:2; % define a time axis starting at 0 and ending at 2 % seconds xx = 2cos(2pi500tt + pi/2); % sinusoid, amplitude 2, frequency % 500~Hz, phase pi/
1.15 Transpose and Single Quote
- Use the single quote (’) after a variable to turn row vectors into column vectors and column vectors into row vectors.
- Works with matrices as well, columns become rows and rows become columns.
>> A = [1 1 1 1; 2 2 2 2; 3 3 3 3; 4 4 4 4]
A =
>> A’
ans =
- In addition, the single quote is used to create strings.
- Single quotes on either side of text creates a string of the characters inside the quotes.
>> T = L(4, 5)
Index exceeds matrix dimensions
- Using the colon operator or square brackets, it is possible to refer to a range of elements in a matrix or vector.
- X([1 2 3]) creates a vector consisting of the first three elements of X.
- L(1,:) extracts the first row of the matrix L.
- Similarly, L(:,1:2) extracts the first two columns of L.
1.17 Array Dimensions
- The commands size and length can be used to find the number of elements of a matrix or vector.
- size(X) returns a vector containing the number of rows and columns in vector X.
- For vectors, the function length returns the number of elements in the vector.
