Matlab Programming for Engineers

CH3: BRANCHING STATEMENTS

Mechanical Engineering Department

MATLAB PROGRAMMING FOR ENGINEERS

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Matlab Programming for Engineers Matlab Programming for Engineers

Dr. Nidal Farhat

Introduction to MatlabIntroduction to Matlab Matlab Basics Matlab Basics Branching StatementsBranching Statements Loops Loops User Defined Functions User Defined Functions Additional Data Types Additional Data Types Input/Output Functions Input/Output Functions Simulink Toolbox Simulink Toolbox Important Toolboxes (if time is available) Important Toolboxes (if time is available)




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OBJECTIVES

The Logical Data Type Relational Operators (==, ~=, >, < , >=, <=) Logic Operators (&, &&, |, ||, xor, ~) Logical Functions (ischar, isempty, ….) Branches

(if-else) Statement switch Statement try-catch Statement

Additional Plotting Features




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THE LOGICAL DATA TYPE (true, false)




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RELATIONAL OPERATORS (==, ~=, >, < , >=, <=)

Some relational operations and their results




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RELATIONAL OPERATORS (==, ~=, >, < , >=, <=)

Compare array by a value

Compare array by another one (of the

same size)

Be careful because of roundoff errors




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LOGIC OPERATORS

Operator Operation& Logical AND (scalar/array, both sides evaluation)

&& Logical AND (scalar, left then right side evaluation)

| Logical inclusive OR (scalar/array both sides evaluation)

|| Logical inclusive OR (scalar, left then right side evaluation)

xor Logical exclusive OR~ Logical NOT




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LOGIC OPERATORS

EXAMPLE




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LOGICAL FUNCTIONS




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QUIZ!




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Branches:

a) if Statement




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BRANCHES (if-STATEMENT)

Optional




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Example: Write a program that determine whether a quadratic equation:

has real (identical/different) or complex roots. (Use input command for entering the coefficients (a,b,c) and disp commands to display the output).

Write a program that calculates the roots in each case. (Use input command for entering the coefficients of the equation and disp commands to display the output).

Test the program on the following equations:




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Example: evaluating a Function of Two Variables

Test it using the following (x,y) values:




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Nested if-Statements

It is preferable to use if-else-end statement whenever is possible




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Branches:

b) switch Statement




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BRANCHES (switch-STATEMENT)

The switch statement syntax is a means of conditionally executing code. In particular, switch executes one set of statements selected from an arbitrary number of alternatives.

The switch_expr and case_expr may be a scalar or a string

Optional




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Remarks: The case expression could be more than one enclosed by {}

At most one code block can be executed. If the switch_exp matches more than case_exp the first one is executed.




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Example:




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Example:

Example




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Example




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Branches:

b) try/catch Statement




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BRANCHES (try/catch)

The try/catch statement is designed to trap errors. In MATLAB when an error is encountered while running the program

the program execution is aborted. Use try/catch statement to run a part of the program susceptible to

produce error when executed. MATLAB will try to execute this part. If an error is produced, then instead of aborting, it executes the part of the program found in the catch statement.

If no error is produced in the try block, the catch block will not be executed.

The programmer can handle errors in the program without causing the program to stop.




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Example




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fprintf command

fprintf(format,data)




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Additional plotting features

Example f(x) = sin(x), from -2π to 2π

Then restrict the axes to the region 0 ≤ x ≤ π, and 0 ≤ y ≤ 1




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Plotting Multiple Plots on the Same Axes

OR




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Creating Multiple Figures




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Subplots Subplot(m,n,p) ≡ creates mxn subplots in the current figure (array of

subplots), m rows and n columns. p is the current subplot.

p=1 p=2

p=4 p=[5 6]

p=3




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Enhanced Control of Plotted Lines

plot(x,y,'PropertyName',value,…)




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Enhanced Control of Plotted Lines Example,




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Enhanced Control of Text Strings




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Additional plotting featuresEn

hanc

ed C

ontr

ol o

f Tex

t Str

ings




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Enhanced Control of Text StringsExamples:




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Polar Plotspolar(theta,r)

Example,




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Polar Plotspolar(theta,r)

Solution:

Matlab Programming for Engineers

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