1. Introduction to MATLAB
Session 2
Flow control
String evaluation
Mihaela Duta
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

2. Today’s topics Flow control Logical operators Relational operators
Logical indexing
Flow control statements
String evaluation
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

3. Logical operators and, or, negation, xor (exclusive or) Two typesb
a xor b 1
and, or, negation, xor (exclusive or)
Two types
Element-wise
Bit-wise
and or
negation
xor
Element-wise
& | ~
Bit-wise
bitand
bitor
bitcmp
bitxor
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

4. Relational operators Perform comparisons
Output variables of logical type:
true = logical(1) – if the relation holds
false = logical(0) – if the relation doesn’t hold
They are:
a < b
a less than b
a <= b
a less than or equal to b
a > b
a greater than b
a >= b
a greater than or equal to b
a == b
a equal to b
a ~= b
a not equal to b
In the previous session we have worked with arithmetical operators. quantitative operations on the operands
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

5. How to apply relational operators
Two matrices of equal dimensions:
to each corresponding element
A matrix and a single value:
to each matrix element in turn compared with the value
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

6. Logical indexing positional indexing use logical arrays
>> b = a( logical([ ]) );
equivalent to
>> b = a(2);
example: output of relational operators
>> cmp = a > 30;
>> a(cmp)
>> a = [ ];
>> a>2
ans =
>> a(a>2)
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

7. Flow control
a series of MATLAB commands are executed in the order they appear
to alter the order and allow for branching we have to use flow control statements:
if-else
switch
for
while
break & return
a = 2; b=4; b=5;
a = 5; disp(‘a is greater than 3’); disp(‘a is less than 3’)
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

8. if-else Syntax Steps: evaluate <logical-expression>
if <logical-expression>
<statement series 1>
else
<statement series 2>
end
Steps:
evaluate <logical-expression>
if true, then execute <statement series 1>
if false, then execute <statement series 2>
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

9. switch Syntax Steps: evaluate <variable/expression>
switch <variable/expression>
case <value 1>
<statement series 1>
etc
case <value n>
<statement series n>
otherwise
<statement series n+1>
end
Steps:
evaluate <variable/expression>
check the result against several options <value i> - labels for the case branches
execute the series of statements corresponding to one case label
if none of the options is valid, then the set of statements corresponding to label otherwise is executed
Equivalent to a series of if statements
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

10. for
Syntax
for <variable> = <start>:<step>:<stop>
<series of statements>
end
Steps
assign to <variable> the value <start> and execute the <series of statements> once
add <step> to <variable> and execute <series of statement> again
repeat the previous step till <variable> reaches the value <stop>
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

11. while
Syntax
while <expression>
<series of statements>
end
Steps
Evaluate <expression> and if true execute the <series of statements> once
Repeat the previous step till <expression> becomes false
If the statements inside the loop do not modify <expression>, we’ll have infinite looping because <expression> will never invalidate
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

12. break and return
break is used inside a for or while loop to request the immediate and unconditional exit from the loop
return causes the immediate exit from a function
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2

13. String evaluation [out1, ...]= eval(<str_with_statement>)
where str is a string containing a statement
the MATLAB interpreter executes the statement stored
[out1, …] = feval(<string_fctname>, in1, …)
the MATLAB interpreter executes function given by <string_fctname> with input arguments in1, … and output arguments out1, …
MSc in Mathematical and Computational Finance Introduction to MATLAB
Session 2