Transcript MatLab – Palm Chapter 3, Part 1 Files, Functions, and Data

MatLab – Palm Chapter 4, Part 2
The if and switch structure
Class 10.1
Sections: 4.4 and 4.6
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RAT 10.1
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Take out a piece of paper, write your name, team #,
today’s date and RAT 10.1 .
As an INDIVIDUAL, you have 2-minutes to determine the
value of y in the MatLab code shown below.
x = 10;
if x >= 12
y = sqrt(x);
else
y = x^2;
end
Pass your answer to the center aisle
Answer: y = 100
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Learning Objectives
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Students should be able to:
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Use conditional statements to develop
logical program flow.
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if, elseif, and else commands
switch structure
Develop flow charts in standard notation.
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4.4 Conditional Statements
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The MatLab conditional statements enable
us to write programs that make decisions
Understanding the IF-THEN-ELSE logic is
fundamental to all software development.
Make sure that you understand:
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if statement on p. 201
else statement on p. 202/203
elseif statement on p. 205
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LOGICAL CONTROL
PROGRAMMING CONSTUCTS
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A conditional (Boolean) statement is an
expression which tests the validity of a
specified condition
e.g.,
z = I ==J
z=I>J
These are used in selection structures
(conditional statements) to control the
flow of a program.
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LOGICAL CONTROL
PROGRAMMING CONSTRUCTS
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Syntax of the if statement:
if logical expression
statements
end
Proper indentation is MANDATORY or
you will receive NO CREDIT!
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Note you can right click and choose smart
indent in the m-file editor.
See page 187 for a flow chart
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LOGICAL CONTROL
PROGRAMMING CONSTRUCTS
Flowchart
representation of the
if statement.
Conditional
statement
Figure 4.1–2
Sequential
Statement(s)
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LOGICAL CONTROL
PROGRAMMING CONSTRUCTS
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MATLAB starts at the beginning of the if
sequence
It proceeds one condition to the next
When it finds a true statement, the
appropriate section of the code is
executed
THE SEQUENCE IS THEN TERMINATED!!!
The last section of code is closed using the
keyword end
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EXAMPLE
x = some given value
if x >= 0
y = sqrt (x)
end
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EXAMPLE
x = 10;
y = 20;
if x >= 0 & y >= 0
z = sqrt(x) + sqrt(y);
w = log(x) – 3*log(y);
end
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LOGICAL PROGRAMMING
CONTRUCTS
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Nested “if” statements:
if logical expression 1
statement group 1
if logical expression 2
statement group 2
end
end
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Nested
Statement
Note the indentions – an absolute must
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Typical flow Chart for
nested if…end Logic
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LOGICAL PROGRAMMING
CONTRUCTS
THE else STATEMENT:
If two mutually exclusive actions can occur as a result
of a decision, use the else statement.
if logical expression
statement group 1
else
statement group 2
end
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See page 204 for a flow chart of a typical if-else
structure.
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LOGICAL PROGRAMMING
CONTRUCTS
Write these
words
Flowchart of the
else structure.
Figure 4.4–2
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In-class Exercise (5 minutes)
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Suppose y = x1/2 for x >= 0
and y = ex – 1 for x < 0
Write a program (.m script file) to
calculate y assuming that x already has
a scalar value.
Test your program for x = 3 and x = -2.
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SOLUTION (Script File)
% Solution to In-Class Exercise
if x >= 0
y = sqrt (x);
else
y = exp (x) -1;
Did you indent
end
properly?!
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LOGICAL PROGRAMMING
CONSTRUCTS
The elseif statement:
When three actions can occur as a result
of a decision, the else and elseif
statements are used along with the if
statement.
Remember: ONLY ONE ACTION WILL
ACTUALY OCCUR!!!
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LOGICAL PROGRAMMING
CONSTRUCTS
if logical expression 1
statement group1
elseif logical expression 2
statement group 2
else
statement group 3
end
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if part
elseif check
else is here
Note: else is
NOT a
conditional
statement
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EXAMPLE
Given:
y = ln x for x > 10
y = x1/2 for x >= 0 and x <= 10
y = ex – 1 for x < 0
Compute y if x has been assigned a scalar
value.
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SOLUTION (Script file)
% Solution to example
if x > 10
Does the order
that I check
y = log (x)
things matter?
elseif x >= 0
YES!
y = sqrt (x)
else
y = exp (x) -1
end
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LOGICAL PROGRAMMING
CONSTRUCTS
As a TEAM, take three minutes to
complete the following exercise.
Write the syntax for the if-elseif-else-end
construct if there are more than three
alternatives.
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SOLUTION
if logical expression1
Statements group1
elseif logical expression2
Statements group2
elseif logical expression3
Statements group3
elseif logical expression4
Statements group4
…
else
Statement if all other cases are false
end
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In-class Assignment 10.1-1
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As an INDIVIDUAL, you have 10 minutes.
Write an .m script file that converts a numerical
test score to a letter grade.
(90 –100) – A
(80 – 89) – B
(70 – 79) – C
(60 – 69) – D
Less than 60 – F
Test your program for the grades of 95 and 72.
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SOLUTION (Script file)
% Program grades.m
grade = 72;
if grade >=90
letter = 'A'
elseif grade >= 80
letter = 'B'
elseif grade >= 70
letter = 'C'
elseif grade >= 60
letter = 'D'
else
letter = 'F'
end
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4.6 The switch Structure
THE “switch” STATEMENT:
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Provides a convenient way to execute
conditional code when there are many
cases to choose from.
This construct can replace series of ifelse-end statements
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LOGICAL PROGRAMMING
CONSTRUCTS
SYNTAX:
switch expression (scalar or string)
case value1
statement group 1
case value2
statement group 2
…
otherwise
statement group n
end
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EXAMPLE for “switch”
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Suppose you are given a variable angle
in degrees to represent the following
directions: Northeast, Southeast,
Southwest, and Northwest.
Use the switch statement to display the
desired direction given the angle.
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SOLUTION
switch angle
Decision variable name
case 45
Value to test
disp('Northeast')
case 135
disp('Southeast')
case 225
disp('Southwest')
case 315
Default case
disp('Northwest')
otherwise
disp('Direction Unknown')
end
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EXAMPLE #2 for “switch”
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You input a numerical value of a
quantity in one set of units (e.g.,
centimeters) and you desire an output
in another set of units (e.g., inches,
feet, or meters, etc…).
Write a program using the switch-case
construction that transforms a length in
centimeters, inches, feet, meters, etc…
to length in centimeters
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SOLUTION
switch units
case {'inch','in'} % ‘units’ contains type of
y = x*2.54;
% input, output is in cm
case {'feet','ft'}
y = x*2.54*12;
case {'meter','m'}
y = x*100;
case {'centimeter','cm'}
y = x;
case {'millimeter','mm'}
y = x/10;
otherwise
disp(['Unknown Units: ' units])
y = NaN;
end
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Assignment 10.1
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Individual assignment.
Due: Nov. 9, 2004
Palm’s MatLab: Chaper 4; #16, 19a,
and 35.
Read Section 4.5 in the Palm MATLAB
book
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