1. Lecture 3 MATLAB programming (1)
Dr .Qi Ying

2. Objectives Data types Logical operators/functions Branching
Debugging of a program

3. A Simple MATLAB program

4. Data types in MATLAB Basic: Advanced (will be discussed later):
Numeric (integer, floating-point, complex)
Logical: True, false
Characters and string
Advanced (will be discussed later):
Structure
Function handles
Look-up table
User-defined data types

5. Logical Data Type Assign a logical data to a variable:
a1 = true; (equivalent to: a1 = 1)
b2 = false; (equivalent to: b2 = 0)
c3 = 5 > 4; % relational operators return logical data

6. Relational operators
Operators with two operands (typically numerical or string) that yield a logical result
A1 OP A2
List of OPs
== equal to
~= not equal to
> greater than
< less than
>= greater than or equal to
<= less than or equal to

7. Relational operators Relational operators on arrays
the result of the operation is an array of logical values
If a1 and a2 are both arrays, they have to be of the same size
It is also valid if one of the operands is a scalar
Relational operators on strings
The strings have to be of the same length
Relational operators are evaluated after all arithmetic operators have been evaluated
7 + 3 < is equivalent to (7+3)<(2+11)
Be careful of round off error when comparing two numerical values
e.g. sin(pi) = e-16 (which is not zero!).

8. Logic operators
Operators with one or two logical operands that yield a logical results
& Logical AND
&& Logical AND with shortcut evaluation
| Logical inclusive OR
|| Logical inclusive OR with shortcut evaluation
xor Logical exclusive OR
~ Logical NOT

9. Short-circuit evaluation
Example: evaluate whether a/b is greater than 10
x = a/b>10.0
Better code to avoid potential “dividing-by-zero” error:
x = (b ~= 0) && (a/b>10.0)

10. Hierarchy of operation
All arithmetic operators are evaluated first
All relational operators are evaluated, from left to the right
All ~ operators are evaluated
All & and && operators are evaluated from left to right
All |, || and xor operators are evaluated from left to right

11. Logical functions isnan(a) true if a is NaN (not a number)
isnumeric(a) true if a is a numerical variable
isinf(a) true if a is Inf

12. Flow control of a program
One of the most important concepts of programming is the ability to control the flow of a program. The mechanisms that allow us to control the flow of execution are called control structures.
Sequence
Branching
Iteration (looping)

13. Branches
Statements that permit selective execution of specific parts of code.
The ‘if’ construct
The ‘switch’ construct
The ‘try/catch’ construct

14. The ‘If’ construct
if control_expr_1 statement 1 statement 2 … elseif control_expr_2 else end
Example:
Solution of a quadratic equation:
r=b^2 – 4*a*c;
if r>0
disp(‘two distinct real roots’);
elseif r==0
disp(‘two identical real roots);
else
disp(‘two complex roots’);
end

15. The ‘If’ construct
Nested ‘if’ construct

16. The ‘switch’ construct
switch (switch_expr) case case_expr_1, statement 1 statement 2 … case case_expr_2, otherwise, end
Example:
switch (value)
case {1,3,5,7,9},
disp (‘The value is odd.’)
case {2,4,6,8,10},
disp (‘The value is even.’)
otherwise,
disp(‘The value is out of range.’)
end

17. Switch Example: [dayNum, dayString] = weekday(date, 'long', 'en_US');
switch dayString
case 'Monday'
disp('Start of the work week')
case 'Tuesday'
disp('Day 2')
case 'Wednesday'
disp('Day 3')
case 'Thursday'
disp('Day 4')
case 'Friday'
disp('Last day of the work week')
otherwise
disp('Weekend!')
end

18. The ‘try/catch’ construct
try statement 1 statement 2 … catch end
Example:
a=[ ];
try
index = input(‘Enter subscript of element to display: ‘);
disp( [ 'a(' int2str(index) ')=' num2str(a(index)) ] );
catch
% if we get here, an error occurred
disp( [ ‘Illegal subscript: ‘ int2str(index) ] );
end

19. Debugging a program
It is equally important to debug as to code. It is very important for new learners to trace through the entire code for variable changes and logic flow to make sure they behave as expected.
Use the debug tool in the editor window.
Set break point at where you would the program to pause to check intermediate results of variables
Execute the program step by step.
Variables and their current values are available at the workspace.

20. Program documentation
% Wixon Valley City Boundary Project
% Lab #2
% file name Wang_Code.m %
% Purpose:
% This program reads in the locations of the boundary corners of the Waxon
% Valley City, Texas, converts them to state plane coordinates, and then
% checks whether random points are inside or outside of an area of interest
% within the city boundary.
% Record of revisions:
% Date Programmer Description of Changes
% ========== ============ ========================
% /3/ B. Wang Original Code
% Define variables:
% points coordinates of boundary corners
% WV-Boundary spherical coordinates of the boundary corners
% p duplicate of the boundary corners with the first
% and last being the identical to make convenient
% drawing c closed shape
% i index variable
% n intermediate variable
% latp latitude coordinates of points
% longp longitude coordinates of points