1. MATLAB
Loops and Branching

2. Loop types Counted loops; called for loop
Conditional loops; called while loop

3. Looping!
Scripts and functions also allow the ability to loop using conventional for and while loops.
Note that the interpreter also lets you do it, it is simply less easy to grasp

4. For Loops Common to other programming languages
for variable = expression
statement
...
end

5. For Loops, con’t: 2 Example: (taken from MATLAB help)
a = zeros(k,k) % Preallocate matrix
for m = 1:k
for n = 1:k
a(m,n) = 1/(m+n -1);
end

6. For Loops, con’t: 3
The looping variable is defined in much the same way that we defined arrays/vectors.
Ex. m = 1:k
Or m = 1:10

7. For Loops, con’t: 4 Loops are shown to end by the keyword “end”
Curly braces are not present to subdivide packets of code
Make use of adequate white-space and tabbing to improve code readability

8. While Loops Similar to while loops in other languages while condition
statement …
end

9. While Loops, con’t: 2 Ex. (taken from help while) while (1+eps) > 1
eps = eps/2;
end

10. While Loops, con’t: 3 Same notes apply to while loops.
Code is separated by the keyword “end”

11. Looping conclusion Some other aspects of looping exist
Use help while and help for to see them

12. LOGICAL CONTROL PROGRAMMING CONSTRUCTS
Syntax of the if statement:
if logical expression
statements
end

13. EXAMPLE
x = some given value
if x >= 0
y = sqrt (x)
end

14. EXAMPLE x = 10; y = 20; if x >= 0 & y >= 0
z = sqrt(x) + sqrt(y);
w = log(x) – 3*log(y);
end

15. LOGICAL PROGRAMMING CONTRUCTS
Nested “if” statements:
if logical expression 1
statement group 1
if logical expression 2
statement group 2
end
Note the indentions
Nested
Statement

16. 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

17. In-class Exercise (5 minutes)
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.

18. SOLUTION (Script File)
% Solution to In-Class Exercise
if x >= 0
y = sqrt (x);
else
y = exp (x) -1;
end
Did you indent
properly?!

19. 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!!!

20. LOGICAL PROGRAMMING CONSTRUCTS
if logical expression 1
statement group1
elseif logical expression 2
statement group 2
else
statement group 3
end

21. 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.

22. SOLUTION (Script file)
% Solution to example
if x > 10
y = log (x)
elseif x >= 0
y = sqrt (x)
else
y = exp (x) -1
end
Does the order
that I check
things matter?
YES!

23. LOGICAL PROGRAMMING CONSTRUCTS
Write the syntax for the if-elseif-else-end construct if there are more than three alternatives.

24. 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