Transcript Document
Matlab Workshop
7/16/2015
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Useful links
http://statlab.stat.yale.edu/help/FAQ/matlab_FAQ.jsp
The help links on this page include
Mathworks’ Getting Started (the official online
documentation of Matlab)
Kermit Sigmon’s MATLAB Primer (a very good
beginner manual);
University of Utah’s MATLAB Tutorial and some
others.
MATLAB’s online help manual
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What is MATLAB?
MATLAB is a matrix-based tool for numerical
computations. It’s very powerful and easy to use.
Both programming language and interactive
environment
Very fast native functions; very slow when
processing loops
Lots of available toolboxes
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Acquiring Matlab
www.yale.edu/software
Free for Yale students
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Launching Matlab
Click “MATLAB 7” from the start menu
(on Unix systems: type “matlab” to enter
interactive mode)
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The Interface
Main Window: Input/Output
Workspace: consists of the variables you create
during a MATLAB session;
Command History: double click them to evaluate
them;
Current Directory browser: shows you where you are.
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Tips
Can use Matlab as a calculator
Type “help” for a list of all help topics
help abs gives the syntax and information about
the absolute value command
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Entering Matrices
Matrices can be
Entered manually
A = [1 2 3 ; 4 5 6 ; 7 8 9]
Generated by built-in functions
Loaded from a file
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Matrix operations:
+ addition
- subtraction
* multiplication
^ power
‘ transpose
\ left division, / division
x = A \ b is the solution of A * x = b
x = b / A is the solution of x * A = b
To make ‘*’ , ‘^’, ‘\’ and ‘/’ apply element-by-element,
we precede the operators by ‘.’
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Subscripts:
Subscripts: the element in row i and column j of
A is denoted by A(i, j).
i,j can also be vectors of indices or logical arrays:
A=4*[1 2 3 4 5 6 7 8 9]’
b=A>18; c=[5 6 7 8 9]’
A(b), A(c)
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The Colon Operator ‘:’
The colon ‘:’ is one of MATLAB ’s most important
operators. It has many formats:
Subscript expressions involving colons refer to portions
of a matrix:
A(5:9) is the fifth to the ninth elements of A.
[0:0.2:3] is a row vector containing integers from 0 to 3,
in increments of 0.2
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Matrices and Random Numbers:
Four functions that generate basic matrices:
Zeros: all zeros. A = zeros(1,3)
Ones: all ones. A = ones(2,4)
Rand: elements are U[0,1] random variables
A = rand(3,5)
Randn: elements are standard-normal random variables
A = randn(2,5)
Be careful: Matlab always sets the same seed.
Get ‘more random’ numbers by typing
rand('state', sum(100*clock))
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A=eye(3) gives a 3-by-3 identity matrix
sparse(m,n): same as zeros(m,n), use if
most elements are zeros.
Concatenation: join small (compatible)
matrices to make bigger ones:
B = [A A-2; A*2 A/4]
Deleting rows and columns:
B(:,2) = [ ]
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Suppressing Output:
If you simply type a statement and press Enter,
MATLAB automatically displays the results on screen.
If you end the line with a semicolon ‘;’, MATLAB
performs the computation but does not display any
result.
Example: C = randn(5,1) v.s.
C = randn(5,1);
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Functions:
MATLAB provides a large number of standard
elementary mathematical functions, including abs,
sqrt, exp, sin.
For a list of the elementary mathematical functions,
type:
help elfun
For a list of more advanced mathematical and matrix
functions, type
help specfun
help elmat
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Programming with MATLAB:
Files that contain code in the MATLAB
language are called M-files. You can create Mfiles using the matlab editor, then use them as
you would any other MATLAB functions or
commands. There are two types of M-files:
Scripts and Functions.
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Scripts
Scripts: a bunch of code grouped together; doesn’t
accept argument or return output.
Example
open m-file editor
type disp(‘Hello’)
save as test.m in your current directory
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Functions:
Functions are M-files that can accept input
arguments and return output arguments. The
name of the M-file and of the function should
be the same.
For example, save this as area.m:
function ar = area(radius)
ar=pi*radius^2;
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Flow Control:
MATLAB has following flow controls:
If statement
For loops
While loops
Continue statement
Break statement
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if … elseif … else … end
if A > B
'greater'
elseif A < B
'less'
else
'equal'
end
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for … end
beta=0.925;
a=1:1000;
for i = 1:1000
betavec(i)=beta^a(i)
end
But you should avoid for loops if possible
newbetavec(a)=beta.^a
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Graphics: plot
x = [0 : .01 : 2*pi];
y = sin(x);
plot(x,y)
y2 = sin(x-.25)
y3 = sin(x-.5)
plot(x,y,x,y2,x,y3)
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Learn from others
There are lots of Matlab functions already out
there:
Search the internet for them!
http://www.mathworks.com/matlabcentral/
James LeSage’s econometrics toolbox:
http://www.spatial-econometrics.com/
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