If you have an AAE account, log in as usual. If you do not have an AAE account you can login using a guest account using the username and password displayed throughout the HECC lab. (Please note: guest users are not allowed to access the REMOTE server.)
(This adds 16 and 15 and shows the value of y)
Note that with a trailing semicolon no output is shown.
3. WRITING AND RUNNING A MATLAB PROGRAM.
As implied the above, you can undertake various tasks using MATLAB one command at a time (i.e., interactive mode) or by running a collection of commands at once contained within a single command file (i.e.; batch mode). To run a file in batch mode you first create an ASCII (or text) file containing these commands. This is often referred to as a script file. This file can be created using your own favorite ASCII file editor (e.g., Notepad++, Tedit, etc) or you can use the native MATLAB program editor. Using the native MATLAB editor is very useful as it checks your syntax as you create the command file. MATLAB expects all script files containing MATLAB commands end with an “m” extension. I highly recommend that you follow this convention.
Let’s assume that you will be using the MATLAB editor. Once MATLAB is started click on the New Script icon. This will open up an editor window where you can write an entire program and run these commands using a single invoking of the file.
The first example we will use is contained in the file example_1.m . This file is contained in the location indicated at the right:
Click on the icon to now open the file you want. You should see something like the following: (Note, the underlined items are native MATLAB commands):
FYI: a few general comments about the code.

There need not be a semicolon to end every command. If you have a semicolon the result of the command will not be shown.

If a statement does not fit on one line, use an ellipsis (three periods), ..., followed by the Enter key to indicate that the statement continues on the next line. A good practice to adopt is that if your command line is more than 80 characters, continue with your code on a 2^{nd} line, indent, and keep typing.

Any variable to the left of an equals sign is a name I made up, e.g. that I want to define for MATLAB

Anything to the right of an equals sign is either a variable name I already defined by a previous command or a MATLAB command/operation/function/reserved word/etc.

Comments, that don’t impact the operation are located after the “%” . You should adopt a policy of using comments extensively in your code.
The MATLAB editor has the normal Windowsbased file management system so you can edit and save this file like any other program you have used before if you are a Window$ user (I assume the same is true for Mac users). I would recommend that you save this file to your private network directory or your own removable storage device. In the editor, save the file by clicking on the following icon in the Editor tab: and save it in the desired location.
With your cursor located in the MATLAB editor window, run this file by clicking on the following button located in the editor toolbar, or simply type the name of the file in the Command Window and hit the Return key.
What happened? Is the matrix c what you expected it to be?
Now in your edit window, add the following to the end of your program. What do you expect it to do?
d=a*b
Save the file and run the program again and notice what happens it doesn’t work. That is, you receive the error message in the bottom window that looks similar to the following:
If you run the program in batch mode you get the following:
The number in parenthesis provides the line number that generated the error. Although I won’t go over it here, you may want to learn how to use the program debugger. I will have Sarah review this material in a later lab.
This new command doesn’t make sense since the “a” and “b” matrices are not dimension compatible with respect to matrix multiplication. Given the severity of the error MATLAB did not run the remaining portion of the program after this error. There is a useful message in the command window, though. When you get this message, it is often helpful to verify the dimensions of your matrices. You will find the Workspace window very useful for the debugging of your code. For small arrays, it shows its elements. For larger arrays, it will show its dimension. By default this window is the box in the upper right of your screen but the location can be changed or window minimizes depending on your needs. If you click on an array displayed in the Workspace window the elements of this array is displayed.
The problem with the above MATLAB command “*” performs matrix multiplication, and here you are telling it to multiply a (2x3) matrix times a (2x3) matrix (which you should remember is not possible).
Change the last line to read
d=a .* b
Also add the line
e=a*bʹ % Note the transpose
Run the code again. Does it work? What is different about these? What do these commands do?
4. READING IN A DATA SET
There are a number of methods for reading in datasets into your MATLAB software. You could load native MATLAB datasets (and similar to STATA and SAS datasets) that are binary files that cannot be opened and examined using an ASCII (text) editor. For an overview of how to open a variety of file types in MATLAB refer to the User’s Guide and the Data Import and Export section. For these workshops (and for our assignments) we will load Excel files containing the data. The first row of these files contains the variable names and the remaining rows are the data. DBMSCOPY is a useful program that can transform any ASCII or binary file of a particular type (e.g., SAS, STATA, EXCEL, GAUSS) into any other file type. Besides being able to transform data from one form to another, DBMSCOPY also has the nice characteristic of allowing you to view any type of data, undertake simple data management activities and to obtain descriptive statistics of this data. The DBMSCOPY manual is available online. Feel free to use your own data conversion software if you prefer.
In the zip file I previously emailed you contained our first data set. The data set is called china_00.xls. Unzip this file to your network drive, hard disk or USB storage device.
4.1 Accessing MATLAB Remotely
You can access MATLAB remotely so long as you have internet access and a valid AAE account (If you have a MAC computer you can also access the remote server but I do not know how to do this. Talk to the HECC director for more information.) You can use the Remote Desktop feature of your operating system to connect to the AAE Remote Server. If you are at a remote location, click on START, then PROGRAMS then ACCESSORIES then COMMUNICATIONS then REMOTE DESKTOP CONNECTION. The computer you want to access is our remote servers which have the computer name (address) of: remote.aae.wisc.edu . Once you enter this address, you will then see what looks like another Windows session. What is actually occurring is that your remote machine is in fact starting a session on a virtual Windows machine (i.e., the REMOTE server). You can then login to the remote computer using your AAE username and password. The remote machine is set up exactly (or very similar to) the regular AAE lab machines. This means that you have access to all the programs in the AAE lab from your remote location. Since you are logging in using your AAE account, you have the same drive mappings as you have when you log into a lab machine. This means that so long as your data, programs etc are stored on a network resource, you have access to it from your remote location. In addition if you set the remote access options correctly on your home machine you can access not only the network drives but also your local drives. Refer to the HECC help system for assistance (http://www.hecc.wisc.edu/).
4.2 MATLAB Code for Reading in a Dataset
Now, I would like you to use the 2^{nd} MATLAB command file to illustrate the use of MATLAB, example_2.m. In the MATLAB editor close the previously used MATLAB command file (Note: You can have multiple files open at once if desired). Then open up the file example_2.m in the editor The following is a listing of the commands in this file (MATLAB functions in bold).
clear; % Command to clear memory
clc; % Command to clear the command window
[full_data,varnames,raw] = xlsread('china_00');
%{
Load all data from an excel dataset
variables: fafh, region, fah, percinc
%}
fafh = full_data(:,1);
region = full_data(:,2);
fah = full_data(:,3);
percinc = full_data(:,4);
[numobs,numvars]=size(full_data); % Determine the number of rows
delete('w:\example_1.out') % Deletes a previously created output file
diary('w:\example_1.out'); % Open up a txt file for output
diary off; % Turn off the sending of output to the output file
var_names=char('fafh','region','fah','percinc'); % var_names is a (4 x 1) character array
disp 'I have successfully run the program' % Show this text in the command window
This block of text, or something very similar to it, will be needed at the beginning of virtually all of your MATLAB programs.
What do the above commands do?
clear: A MATLAB command clears the workspace from previous batch runs or command line inputs (http://www.mathworks.com/help/techdoc/ref/clear.html).
clc: A MATLAB command that clears the command window (http://www.mathworks.com/help/techdoc/ref/clc.html)
xlsread: Command to read in a Microsoft Excel spreadsheet file. There are a number of different structures of this command. Below is a listing of these alternative structures obtained from the xlsread help entry:
[num,txt,raw] = xlsread(filename)
[num,txt,raw] = xlsread(filename,sheet)
[num,txt,raw] = xlsread(filename,range)
[num,txt,raw] = xlsread(filename,sheet,range)
[num,txt,raw] = xlsread(filename,1)
[num,txt,raw] = xlsread(filename,sheet,'','basic')
[num,txt,raw,custom] = xlsread(filename,sheet,range,'',functionHandle)
The command [num,txt,raw] = xlsread(filename) reads data from the first worksheet in the Microsoft Excel spreadsheet file named filename and returns the numeric data in array num (this can be any name I want). With this command structure, it optionally returns the variable names in the cell array txt (this can be any name I want), and the unprocessed data (numbers and text) in cell array raw (this can be any name I want). (http://www.mathworks.com/help/techdoc/ref/xlsread.html)
fafh: Created variable containing the (numobs x 1) vector of food away from home expenditures
region: Created variable containing the (numobs x 1) vector of region of residence
fah: Created variable containing the (numobs x 1) vector of food at home expenditures
percinc: Created variable containing the (numobs x 1) vector of per capita income
size: Returns the dimension of the target matrix in separate variables numobs (rows) and numvars (columns). (http://www.mathworks.com/help/techdoc/ref/size.html)
numobs: A created variable (this can be any name I want) that contains the number of observations in the dataset
numvars: A created variable (this can be any name I want) that contains the number of variables in the data matrix
delete: This command is used to delete the named file. If the file does not exist you will receive an error (nonfatal) message. (http://www.mathworks.com/help/techdoc/ref/delete.html)
diary: Is used to write a copy of all subsequent keyboard input and the resulting output (except it does not include graphics) to the named file, where the filename is the full pathname or filename is in the current MATLAB folder. If the file already exists, output is appended at the end of the file. By deleting it first I avoid the appending of output. (http://www.mathworks.com/help/techdoc/ref/diary.html)
diary off: This command suspends the diary command. (Note that diary on resumes diary mode using the current filename, or the default filename diary if none has yet been specified.)
5. RUN THE CODE, AND CHECK TO MAKE SURE YOU HAVE
SUCCESSFULLY LOADED THE DATA
With the above program in the editor, run this file using the main editor menu. In the Workspace area you should see the four vectors of data plus the underlying matrix each with 2050 observations. You should see the following displayed in the Command window: “I have successfully run the program”.
6. IDENTIFY YOUR VARIABLES
The variables in this data set are the following
Description Variable Name
Per Capita Income percinc
At home food expenditures fah
Away from home food expenditures fafh
Region (either 1, 2, or 3) region
The use of the “ : ” in the above command file (e.g., lines 9 – 12) tells MATLAB to grab all the rows of the full data matrix for the particular column of data . If you wanted to grab only the 120^{th} 220^{th} observations for some reason you would type the following:
inc_2 = full_data(120:220,4); or inc_2 = percinc(120:220,:);
If you want to create a (2050 x 2) matrix containing per capita income and region you could enter the following either in your command file or interactively:
income_region=full_data(:,[4 2]);
This would grab the 4^{th} and 2^{nd} columns (the columns associated with PERCINC and REGION) from the full_data matrix using all the observations (which is what the “:” means). I could have created this new variable via the horzcat horizontal concatenation command:
income_region = horzcat(percinc,region);
Note that one can only use horizontal concatenation if the two matrices have the same number of rows. The resulting file will have the sum of the number of columns of the component matrices. (Note, vertical concatenation can be obtained via the use of the vertcat command. In this case to undertake vertical concatenation one needs the same number of columns in the candidate matrices)
In the command window type the following command:
begind=numobs10;
test_data=horzcat(fah(begind:numobs,:),region(begind:numobs,:)) ;
and see what is generated.
FYI: The parentheses attached to the end of a matrix name allow you to specify part of a matrix. For example,
full_data(2,4) is the single element in the 2^{nd} row and 4^{th} column of the full_data matrix
full_data(2,1:3) is the (1x3) vector of element in the 2^{nd} row and 1^{st} through 3^{rd}
columns
full_data(:,4) generates the vector of elements in the entire 4^{th} column of full_data.
7. NOW LET’S DO SOME MATHEMATICAL MANIPULATIONS AND
DATA INTERPRETATION
Let’s do the following simple tasks:
i) What is the average income and food expenditure?
ii) What is the maximum level of income?

What percent of households live in region 1?

What is the minimum, maximum, and average food away from home expenditures in region 1?
****************************************************************
7.A ADDITIONAL COMMANDS YOU FIND USEFUL
A list of commands by category can be obtained from the following URL: http://www.mathworks.com/help/matlab/functionlist.html . An alphabetical list can be obtained via the following: http://www.mathworks.com/help/matlab/functionlistalpha.html . Here are a few commands that you may find useful:
sum(x) returns the sum of the elements in matrix x (http://www.mathworks.com/help/techdoc/ref/sum.html)
cumsum(x) returns the cumulative sum of the columns (or rows) of matrix x
(http://www.mathworks.com/help/techdoc/ref/cumsum.html)
mean(x) returns the mean of every column (or row) of matrix x
(http://www.mathworks.com/help/techdoc/ref/mean.html)
std(x) returns the standard deviation of the elements in each column (or row) of matrix x
(http://www.mathworks.com/help/techdoc/ref/std.html)
min(x) returns the smallest element in each column (or row) of matrix x
(http://www.mathworks.com/help/techdoc/ref/min.html)
max(x) returns the largest element in each column (or row) of matrix x
(http://www.mathworks.com/help/techdoc/ref/max.html)
cov(x) computes the variancecovariance matrix
(http://www.mathworks.com/help/techdoc/ref/cov.html)
zeros(r,c) creates a matrix with r rows and c columns full of zeros
(http://www.mathworks.com/help/techdoc/ref/zeros.html)
ones(r,c) creates a matrix with r rows and c columns full of ones
(http://www.mathworks.com/help/techdoc/ref/ones.html)
eye(N) creates an NxN idendity matrix (you must either use a number in place of N or define N)
(http://www.mathworks.com/help/techdoc/ref/eye.html)
randn(r,c) creates a matrix with r rows and c columns of c independent std. normal random numbers
(http://www.mathworks.com/help/techdoc/ref/randn.html)
sort(x) Sort array elements in ascending or descending order depending on the additional arguments supplied when using this command
(http://www.mathworks.com/help/techdoc/ref/sort.html)
size(x) returns array dimensions
(http://www.mathworks.com/help/techdoc/ref/size.html)
normcdf(x) returns the Prob(z<=x) where z is a N(0,1) random variable (requires Statistics Toolbox)
%{ , %} The text enclosed within the %{ and %} symbols is a comment block. Use these symbols to insert comments that take up more than a single line in your script of function code. Any text between these two symbols is ignored by MATLAB. You can use these to have MATLAB not execute a set of commands.
7.B. Logical Expressions
&, , ~ Element by element logical operations on arrays
Syntax: expr1 & expr2
expr1  expr2
~expr
The symbols &, , and ~ are the logical array operators AND, OR, and NOT. These operators are commonly used in conditional statements, such as if and while, to determine whether or not to execute a particular block of code. Logical operations return a logical array with elements set to 1 (true) or 0 (false), as appropriate.
expr1 & expr2 represents a logical AND operation between values, arrays, or expressions expr1 and expr2. In an AND operation, if expr1 is true and expr2 is true, then the AND of those inputs returns a true value. If either expression is false, the result is false. Here is a pseudocode example of AND:
IF (expr1: all required inputs are included) AND ...
(expr2: all inputs are valid)
THEN (result: execute the function)
expr1  expr2 represents a logical OR operation between values, arrays, or expressions expr1 and expr2. In an OR operation, if expr1 is true or expr2 is true, then the OR of those inputs returns a value of true. If both expressions are false, the result is false. Here is a pseudocode example of the use of OR:
IF (expr1: S is a string) OR ...
(expr2: S is a cell array of strings)
THEN (result: parse string S)
~expr represents a logical NOT operation applied to expression expr. In a NOT operation, if expr is false, then the result of the operation is true. If expr is true, the result is false. Here is a pseudocode example of NOT:
IF (expr: function returned a Success status) is NOT true
THEN (result: throw an error)
The function xor(A,B) implements the exclusive OR operation.
eq Test for equality
Syntax: A == B
eq(A, B)
A == B compares each element of array A for equality with the corresponding element of array B, and returns an array with elements set to logical 1 (true) where A and B are equal, or logical 0 (false) where they are not equal. Each input of the expression can be an array or a scalar value.
If both A and B are scalar (i.e., 1by1 matrices), then the MATLAB software returns a scalar value.
If both A and B are nonscalar arrays, then these arrays must have the same dimensions, and MATLAB returns an array of the same dimensions as A and B.
If one input is scalar and the other a nonscalar array, then the scalar input is treated as if it were an array having the same dimensions as the nonscalar input array. In other words, if input A is the number 100, and B is a 3by5 matrix, then A is treated as if it were a 3by5 matrix of elements, each set to 100. MATLAB returns an array of the same dimensions as the nonscalar input array.
When comparing handle objects, use eq or the == operator to test whether objects are the same. Use isequal to test if objects have equal property values, even if those objects are different.
eq(A, B) is called for the syntax A == B when either A or B is an object.
gt Test for greater than
Syntax: A > B
gt(A, B)
A > B compares each element of array A with the corresponding element of array B, and returns an array with elements set to logical 1 (true) where A is greater than B, or set to logical 0 (false) where A is less than or equal to B. Each input of the expression can be an array or a scalar value.
If both A and B are scalar (i.e., 1by1 matrices), then the MATLAB software returns a scalar value.
If both A and B are nonscalar arrays, then these arrays must have the same dimensions, and MATLAB returns an array of the same dimensions as A and B.
If one input is scalar and the other a nonscalar array, then the scalar input is treated as if it were an array having the same dimensions as the nonscalar input array. In other words, if input A is the number 100, and B is a 3by5 matrix, then A is treated as if it were a 3by5 matrix of elements, each set to 100. MATLAB returns an array of the same dimensions as the nonscalar input array.
gt(A, B) is called for the syntax A>B when either A or B is an object.
ge Test for greater than or equal to
Syntax: A >= B
ge(A, B)
A >= B compares each element of array A with the corresponding element of array B, and returns an array with elements set to logical 1 (true) where A is greater than or equal to B, or set to logical 0 (false) where A is less than B. Each input of the expression can be an array or a scalar value.
If both A and B are scalar (i.e., 1by1 matrices), then the MATLAB software returns a scalar value.
If both A and B are nonscalar arrays, then these arrays must have the same dimensions, and MATLAB returns an array of the same dimensions as A and B.
If one input is scalar and the other a nonscalar array, then the scalar input is treated as if it were an array having the same dimensions as the nonscalar input array. In other words, if input A is the number 100, and B is a 3by5 matrix, then A is treated as if it were a 3by5 matrix of elements, each set to 100. MATLAB returns an array of the same dimensions as the nonscalar input array.
ge(A, B) is called for the syntax A >= B when either A or B is an object.
le Test for less than or equal to
Syntax: A <= B
le(A, B)
A <= B compares each element of array A with the corresponding element of array B, and returns an array with elements set to logical 1 (true) where A is less than or equal to B, or set to logical 0 (false) where A is greater than B. Each input of the expression can be an array or a scalar value.
If both A and B are scalar (i.e., 1by1 matrices), then the MATLAB software returns a scalar value.
If both A and B are nonscalar arrays, then these arrays must have the same dimensions, and MATLAB returns an array of the same dimensions as A and B.
If one input is scalar and the other a nonscalar array, then the scalar input is treated as if it were an array having the same dimensions as the nonscalar input array. In other words, if input A is the number 100, and B is a 3by5 matrix, then A is treated as if it were a 3by5 matrix of elements, each set to 100. MATLAB returns an array of the same dimensions as the nonscalar input array.
le(A, B) is called for the syntax A < =B when either A or B is an object.
lt Tests for less than
Syntax: A < B
lt(A, B)
A < B compares each element of array A with the corresponding element of array B, and returns an array with elements set to logical 1 (true) where A is less than B, or set to logical 0 (false) where A is greater than or equal to B. Each input of the expression can be an array or a scalar value.
If both A and B are scalar (i.e., 1by1 matrices), then the MATLABsoftware returns a scalar value.
If both A and B are nonscalar arrays, then these arrays must have the same dimensions, and MATLAB returns an array of the same dimensions as A and B.
If one input is scalar and the other a nonscalar array, then the scalar input is treated as if it were an array having the same dimensions as the nonscalar input array. In other words, if input A is the number 100, and B is a 3by5 matrix, then A is treated as if it were a 3by5 matrix of elements, each set to 100. MATLAB returns an array of the same dimensions as the nonscalar input array.
lt(A, B) is called for the syntax A < B when either A or B is an object.
ne Test for inequality
Syntax: A ~= B
ne(A, B)
A ~= B compares each element of array A with the corresponding element of array B, and returns an array with elements set to logical 1 (true) where A and B are unequal, or logical 0 (false) where they are equal. Each input of the expression can be an array or a scalar value.
If both A and B are scalar (i.e., 1by1 matrices), then the MATLAB software returns a scalar value.
If both A and B are nonscalar arrays, then these arrays must have the same dimensions, and MATLAB returns an array of the same dimensions as A and B.
If one input is scalar and the other a nonscalar array, then the scalar input is treated as if it were an array having the same dimensions as the nonscalar input array. In other words, if input A is the number 100, and B is a 3by5 matrix, then A is treated as if it were a 3by5 matrix of elements, each set to 100. MATLAB returns an array of the same dimensions as the nonscalar input array.
ne(A, B) is called for the syntax A ~= B when either A or B is an object.
C. Use of FOR LOOPS
The following illustrates the use of a “For Loop”. You should refer to your reference material for instructions concerning its use. It is very important to remember that the use of the For loop can make your life much easier if you are doing repetitive tasks. The For loop is designed to execute statements a specified number of times.
x=zeros(20,1); %{This initializes the x matrix so there are place holders for later use In general this only needs to be done when using for or do loops.%}
for i =1:20; %{ i is an temporary variable used to control the loop In this example
the loop goes from 1 to 20 in increments of 1, e.g., 20 steps %}
x(i)=i; /* the i^{th} element of the vector x is assigned the current value of i */
end; /* end of for loop */
Another way to accomplish the above (without creating a placeholder for “x”):
for i = 1:20;
if i == 1;
x=i;
else; x=vertcat(x,i); /* This vertically concatenates the previous x vector with
another element equal to the current value of “i” */
end;
end;
If I wanted every odd value of x to be 0, I could have done the following:
x=zeros(20,1);
for i =1.0: 2, 20;
x[i]=i;
end;
or
x=zeros(20,1);
for i = 1:10;
jj=(2*i);
x[jj]=jj;
end;
D. RUN THE DEMO_MATLAB PROGRAM
Now you are ready to run a longer MATLAB program. I sent you a 3^{rd} command file with the name demo_matlab.m . I assume you have either saved it in your network drive or in your USB storage device. This file undertakes some basic matrix manipulations. After examining this file, run it in MATLAB and make sure you understand the various operations.
A FINAL NOTE: Try to develop a habit of writing clean and neat code (e.g. use of indentation for loops, lines of code that don’t go on forever, etc). This will facilitate code debugging.
Indenting code makes reading statements, such as for (do while) loops, easier. To set and apply indenting preferences to code in the Editor:

From the main program toolbar choose Preferences > Editor/Debugger > Language

From the Language dropdown menu, select a language

Select or clear Apply smart indenting while typing, depending on whether you want indenting applied automatically, as you type. If you clear this option, you can manually apply indenting by selecting the lines in the Editor to indent, rightclicking, and then selecting Smart Indent from the context menu.

Do one of the following:

If you chose any language other than MATLAB in step 2, click OK.

If you chose MATLAB in step 2, select a Function indenting format, and then click OK. Function indent formats are:

Classic: The Editor aligns the function code with the function declaration.

Indent nested functions: Editor indents function code within a nested function.

Indent all functions — The Editor indents the function code for both main and nested functions.