User Defined Functions
EE 201
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Session Agenda
 Contact before work
5 min.
 User Defined Functions
70 min.
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Class Learning Objectives
 Achieve Comprehension LOL of User
Defined Functions.
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User can create the function
x=5; y= 𝑥 2
Normal Procedure;
y=x^2; % default MATLAB operation
y=25
Function created by user for same
application
function [y]=square1(x)
y=x*x;
end
y=square1(x)
y=25
% by User defined function
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User Defined Functions
-The first line in a function file must begin
with a function definition line that has a
list of inputs and outputs.
-This line distinguishes a function M-file
from a script M-file. It’s syntax is as
follows:
function [output variables]= name(input
variables)
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 function [output variables]= name(input
variables)
 Note that the output variables are enclosed in square brackets [ ],
while the input variables must be enclosed with parentheses ( ).
The function name ( name) should be the same as the file name in
which it is saved (with the .m extension).
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Writing User Defined Functions
You should write this command at the beginning of the m-file and
you should save the m-file with a file name same as the function
name
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Example:
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 Note :Brackets [ ] are optional for one
output
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Example
Only the order of the arguments
is important , not the names
of the arguments:
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 You can use arrays as input
arguments:
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Examples of Function Definition Lines
1. One input, one output:
function [area_square] = square(side)
2. Brackets are optional for one input, one
output:
function area_square = square(side)
3. Three inputs, one output:
function [volume_box] =box(height,width,length)
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Examples of Function Definition Lines
4. One Input, two outputs:
function [area_circle,circumf]=circle(radius)
5. No Input, No output:
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Example
 Write a MATLAB program that
computes area and circumference of
a circle
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 Area =π (radius)2
 Circumference =2π radius
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Solution
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Example
a) ِCreate a MATLAB user defined function
that computes area and circumference of
a circle.
b) Write a MATLAB program that:
-prompt the user to enter the radius in
meter .
- it computes area and circumference using
the function you defined in part (a)
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Local variables
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 The variables x and y are local to the
function S, so unless you pass their
values by naming them x and y, their
values will not be available in the
workspace outside the function. The
variable u is also local to the function.
For example:
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Example:
function v=L(a)
N
b=2;
v=a+b ;
end
>> a=20;
>>b=5;
v=L(a)
v=
22
N
>>a
a=
20
>>b
b=
5
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Example:
function v=L(a)
N
b=2;
v=a+b ;
end
>> x=20;
>>b=5;
z=L(x)
z=
22
>>x
x=
N
20
>>b
b=
5
>> a
??? Undefined function or variable
'a'.
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Quiz
a) ِCreate a MATLAB user defined function that
computes the surface area and Volume of a
Box.
b) Write a MATLAB program that:
-prompt the user to enter the 3 sides of the
box .
- computes the surface area and Volume of
the Box using the function you defined in
part (a)
- Display the results
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Quiz
function [V,SA]=V_S(L,W,H)
V=L*W*H;
SA=L*W*2+L*H*2+H*W*2;
end
L=input(‘Please enter the Length’);
W=input(‘Please enter the Width’);
H=input(‘Please enter the Height’);
[V,SA]=V_S(L,W,H);
disp([‘The Volume is’, num2str(V)])
disp([‘The Surface Area is’, num2str(SA)])
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