The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
MATLAB for the Sciences
The MATLAB Editor, Scripts, and Functions
Jon M. Ernstberger
January 6, 2008
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
The MATLAB Editor
To access the MATLAB editor, simply type “edit” at the terminal.
The editor provides the basic interface for programming in any
form in MATLAB.
This is more than JUST a text editor. You’ll see that.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
MATLAB Scripts
What is a Script?
A MATLAB script is a sequence of commands that has been saved
to a file.
Traditionally saved to files
with extensions “.m”.
Scope: can interact with the
currently available
workspace. Pro or con?
You may have to clear
variables!
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
Exercises
Do a help on “clear”. Create a simple script which adds the
squares of both x and y . In your terminal set x = 2 and
y = 4. What happens if you do or don’t include “clear all” in
your MATLAB script?
Do a help on “zeros”, and a help on “rand”. In a new
MATLAB script named zero test.m make a random matrix
which has dimension 1000 × 1000. Create a matrix of identical
size of zeros. Add, subtract, and multiply these matrices
together. In full sentences in comments, at the top of your
script, describe each “built-in” MATLAB function used and
the intent of this script. In the first three lines of these
comments place your name, the script name, and the date.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
Exercises, cont.
Do a help on “save”. In that same script file listed above,
save the variable workspace to your hard-disk in a .mat file
named “big matrices.mat” using the command in the script
(not using a command through the MATLAB IDE). Heavily
comment this line for future remembrance.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
MATLAB Functions
What defines a mathematical function? (Hint: think domains
and elements.)
What about a function
F (x) : Rn → Rm ?
ex: f (x, y ) = x 2 + y 2 , x 2 − y 2
The idea is “ For one (set of) input(s), there is one (set of)
output(s).”
We often want to define MATLAB “functions” which take
inputs and return non-ambiguous outputs.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
MATLAB Functions, cont.
MATLAB functions take inputs and return the outputs.
Still saved as an m-file.
Functions are to be used for
encapsulating often reused
bodies of code.
Called via
>>x=2;
>>y=sample_function1(x);
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
Multi-input/output functions
I can have multiple inputs and outputs to any MATLAB
function.
This saves the programmer from writing multiple functions
which take the same inputs to output different values.
function [f,g]=pseudo_fcn1(x,y)
f=x^2+y^2;
g=x^2-y^2;
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
A Sample Function
Compute the area of a circle in a function.
A = πr 2
%This function computes the area of a circle.
%Input: radius r
%Output: area
function area=circle_properties(r)
area=pi*r^2;
In-Class Exercise
Download circle properties.m and change this function to also
output circumference.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
More Exercises
Create a function which takes as input a single value or a
vector of values and returns the tangent of that/those values.
You may not use the tan(x) function built into MATLAB.
Name this function hard tan and save it as hard tan.m. Again
heavily comment this piece of code.
Save the above function as hard sec and alter this function to
output the secant and cosecant of x using only the sine and
cosine functions. In your comments, include all of these
changes and be sure to mention which values cannot be input.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
More Exercises, cont.
Create a function called half life. This function should take as
input decay rates, initial amounts of a radioactive substance,
and amount of time the quantity has been decaying. Heavily
comment this function.
Modify this function to output a second argument, the
half-life of the material. Test your results with Neptunium-239
and Carbon-14. (Hint: use Google or Wikipedia.)
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
Comments
What’s the big deal about comments?
Example
% Jon Ernstberger
% 12/22/2008
% Sample Comments
Each comment begins with a “%”.
Everything on a line that starts with the “%” will be
considered a comment.
Helpful Hints:
Do not use short-hand. Use complete sentences.
Always comment!
Comment often.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
The Text Menu
“Comment/Uncomment”. Highlight a body of code and
comment or uncomment those commandlines.
“Increase Indent/Decrease Indent”. Highlight a body of code
and increase or decrease the indentation.
“Smart Indent”. The MATLAB editor should “smartly”
choose the indentation of an indented group of text. Should
be automatic.
“Code Folding”. If you have tons of nested codes, this can
compact your code incredibly for purposes of readability!
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
The Tools Menu
MATLAB Profiler
Useful for identifying trouble points in your code.
The Profiler identifies portions of code which take the longest
periods of time.
Some codes require hours, days, or months of time to run! By
reducing the runtime of the “heavy” portions of code, these
runtimes are highly decreased.
The Profiler also makes suggestions for reprogramming certain
code portions.
We’ll go into more detail at a later point (hopefully).
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
The Window Menu
“Split-screen”. Helps you see and compare bodies of code in
conjunction.
Tiling of windows is useful to keep more than two files open
for editing or comparison.
Programming Hint
Use “Left/Right Split Screen” in order to edit scripts and
functions. This helps the programmer see the most code possible.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
In-Class Assignments
1
Write a MATLAB function named temp convert which takes
as input temperature in Fahrenheit and outputs the conversion
in degrees Celsius. How can you test to make sure it works?
2
Write a MATLAB script which evaluates the temperature at
95◦ and −44.5◦ Fahrenheit.
3
Modify your function temp convert to have a second output
for degrees Kelvin.
4
Rerun Problem 2 to test your answers.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
Take Home Assignments
1
2
The maximum height of a projectile with initial velocity
V
A
2
2
fired at angle A radians above the horizon is V sin
2g
2
where g = 9.81m/s . What is the maximum height reached
by a rock from a volcano ejected at 700 m/s at an angle of
60◦ ?[1] (Hint: Type help sin.)
The difference formula is given as
f (x + h) − f (x)
h 6= 0.
h
Set h = 1 × 10−5 and let f (x) = x 2 + 2x + 1. Write a
MATLAB function for f (x) named quadratic fcn1 which takes
as input x and outputs f (x). Write a MATLAB script named
quadratic fcn1 eval to evaluate the difference quotient for
f (x) at x = 10, x = 20, and x = 1000.
Jon M. Ernstberger
MATLAB for the Sciences
The MATLAB Editor
Scripts and Functions
The MATLAB Editor, Cont.
Assignments
References
References
S.L. Edgar.
Fortran for the’90s: problem solving for scientists and
engineers.
Computer Science Press New York, NY, 1992.
Jon M. Ernstberger
MATLAB for the Sciences