Logical Operations In Matlab - PowerPoint Presentation

Slide1

Logical Operations

In MatlabSlide2

Booleans

Booleans are a class of variable that have values of 0 or 1.

0 = false

1 = true

George Boole

(1815-1864)Slide3

Booleans

Using the code on the right, we can set the value of two variables (a and b) and then ask Matlab if they are equal to each other using “==“

Matlab returns 1 if they are equal and 0 if they are not.Slide4

Booleans

In this case,

a

is not equal to b, so Matlab will return 0.Slide5

Booleans

Similarly, you can ask Matlab whether one variable is greater than another using “>”

Here Matlab will return 1Slide6

Booleans

Here, Matlab will return 0Slide7

Booleans

Similarly, the “<“ sign can be used to test whether one variable is less than another

Here Matlab will return 1Slide8

Booleans

Here Matlab will return 0Slide9

Booleans

You can also compare two variables to see if one is greater than or equal to the other using “>=“

Here Matlab will return 1Slide10

Booleans

Here Matlab will again return a 1Slide11

Booleans

Here Matlab will return 0Slide12

Booleans

Similarly, we can ask Matlab whether or not one variable is less than or equal to another using “<=“

Here Matlab will return 1Slide13

Booleans

Here Matlab will also return 1Slide14

Booleans

Here Matlab will return 0Slide15

Booleans

Characters can also be compared using the above-mentioned operators.Slide16

Booleans

For strings, using Boolean operators compares each element of the string and returns a 1 or 0 for each comparison.Slide17

Booleans

If we want to know if the entire string for one variable is the same as for another variable then we need to use

strcmp

.Slide18

Booleans

Using

strcmp

, if even one letter is different, it will return 0Slide19

Booleans

Boolean operations also work on arrays and matrices.Slide20

Boolean Indexing

You can also use Boolean variables to index other variables.Slide21

Boolean Indexing

This can be a very nice shot-hand way to extract data of interest.Slide22

Boolean Indexing

Boolean operations may be combined using “&”Slide23

Boolean Indexing

Boolean operations may also be combined using | (for “or” statements).Slide24

if Statements

If statements take Boolean arguments (e.g. a<b).

If the Boolean is true, then the code after the if statement is executed.Slide25

if Statements

If statements take Boolean arguments (e.g. a<b).

If the Boolean is true, then the code after the if statement is executed.

Otherwise Matlab checks to see if the

elseif statement is true. If it is then Matlab executes the code immediately after the elseif statement. (You can have multiple elseif statements between the if and the else statement).Otherwise, the code after the “else” statement is executed.Slide26

if Statements

Here’s an example with multiple

elseif

statements.Slide27

Switch Statements

Switch

statements take string arguments (e.g. ‘Tuesday’).

For each

case, Matlab compares the string beside the switch statement (our Day variable in this case) with the strings beside the case statements until it finds a match. Then it executes the code for the matching

case

.

If no match is found, then it executes the code found under the

otherwise

statement.Slide28

While loops

A

while

loop executes as long as its Boolean argument is true.

In this example, the while loop will add 1 to n until n stops being less than 5.Slide29

For loops

A

for

loops executes for a fixed number of times.In this case, it will cycle through 5 times and at each cycle tell us which number it is on.Slide30

Embedding

Logical structures can be embedded within each other.

Matlab automatically indents logical statements so that the start of the statement lines up with its end.