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Chapter 3 Branching Statements and
Program Design
Introduction to Top-Down Design Techniques
Use of Pseudocode
The Logical Data Type
Branches
Additional Plotting Features
More on Debugging MATLAB Programs
Summary
Exercises
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Chapter 3 Branching Statements and

Program Design

  • Introduction to Top-Down Design Techniques
  • Use of Pseudocode
  • The Logical Data Type
  • Branches
  • Additional Plotting Features
  • More on Debugging MATLAB Programs
  • Summary
  • Exercises

Introduction

  • Sequential programs
    • Reading input data, process it to produce a desired answer, print out the answer, and quit.
    • There is no way to repeat sections of the program more than once
    • There is no way to selectively execute only certain portion of the program depending on values of the input data.
  • We will introduce a number of MATLAB statement
    • Allow us to control the order in which statements are executed in a program. - Branches : select specific sections of the code to execute - Loops : which cause specific sections of the code to be repeated. (Chapter 4)
  • We will introduce a top-down design techniques.
  • We will introduce pseudocode algorithm.

Matlab Matlab

Top-Down Design

  • Clearly state the problem that you are trying to solve.

(Page 88)

  • Define the inputs required by the program and the outputs

to be produced by the program. (Page 89)

  • Design the algorithm that you intend to implement in the

program. (Page 90)

  • Algorithm: a step-by-step procedure for finding the solution to a problem.
  • Stepwise refinement: pseudocode.
  • Turn the algorithm into MATLAB statements.
  • Test the resulting MATLAB program.

3.2 Use of Pseudocode

• Pseudocode is a hybrid mixture of

MATLAB and English.

• Pseudocode is intended to aid you in

organizing your thoughts before converting

them into MATLAB code.

– Example 2.3 (page 64)

– Pseudocode (page 93)

3.3 The Logical Data Type

• true or false

• MATLAB operators

– Relational operator

– Logic operator (single byte)

  • Relational operators may be used to compare a scalar value with an array.

Relational operators can only compare two strings if they are

of equal lengths. (see chapter 6)

== symbol is a comparison operation that return a logical result

= symbol is a assignment operation

7 + 3 < 2 + 11 is equal to (7 + 3) < ( 2 + 11)

  • A caution about the == and ~= operators
    • For string comparison is safe
    • For numeric is not safe
      • Due to roundoff errors
  • Logical ANDs: && and &
    • Difference 1
      • && supports short-circuit evaluations
      • && will evaluate expression l1 and immediately return result
      • if l1 is false , never evaluates l
      • & evaluates both l1 and l2 before returning an answer
    • Difference 2
      • && works between scalar values
      • & works with either scalar or array values, as long as the sizes of the arrays are compatible

faster

x = a / b > 10.0 b = 0, x =? x = (b ~= 0) && (a/b > 10.0)

  • Logical inclusive ORs: || and |
    • Difference 1
      • || supports partial evaluations
      • || will evaluate expression l1 and immediately return result
      • if l1 is true , never evaluates l
      • | evaluates both l1 and l2 before returning an answer
    • Difference 2
      • || works between scalar values
      • | works with either scalar or array values, as long as the sizes of the arrays are compatible
  • Using numeric data with logic operators
    • Real numeric data can be use with logic operators
      • ~5 is false, ~0 is true
    • Logic operators may be used to compare scalar value with an array.
    • Logic operators may be used to compare two arrays with same size
    • Logic operators may not be used with complex or imaginary numeric data - 2i & 2i will produce an error when it is evaluated
  • Hierarchy of operations
    • All arithmetic operators are evaluated first in the order

previously described.

  • All relational operators (==, ~=, >,>=,<,<=) are

evaluated, working from left to right.

  • All ~ operators are evaluated.
  • All & and && operators are evaluated, working from

left to right.

  • All | and || , and xor operators are evaluated, working

from left to right.