cz1102 computing & problem solving lecture 12

8/8/2019 CZ1102 Computing & Problem Solving Lecture 12

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Review

Week 14

By JI, Hui


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Exam

Closed book, two A4 sizes double-sides help

sheet are allowed

Exam time 2 hours

No calculator or computer is allowed.

Totally 6 questions


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Questions

Determine which the commands is valid or not e.g. A?=7+1.5

Find the value of the expression e.g. [1 3] .* [1 ,4]

What is displayed when the block of code is executed e.g. a=0;

for k = 1:4

a = a + 2*k;

end;

disp(a);

Write a function such that it takes ***** as input andoutput its ********


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Variable

Rule for name of variable

consist only of the letters az, AZ, the digits 09

and the underscore _

Starting with a letter

Reserved wordcan not be used as the variable

name

Matlab is case sensitive Matlab distinguishes between upper- and lower-case

letters.


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Assignment

Format of variable assignment

variablename = expression

Expression is executed and store the result in

variablename

= does not mean equal, it means store

A semicolon in the end of expression will

suppress the output


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Expression

Allowable items in expression

Values

Variables (already defined)

Operators

Pre-defined functions

Matlab

User

Parenthesis


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Precedency of operators

Precedency of operators (from the first to the last)1. ()

2. ^

3. - (Negation)

4. *,\,/5. +,-

Within the same precedency level Expression is evaluated from right to left

Question: what is the value of a*b/c?

Nested parenthesis Inner parenthesis is evaluated first


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Data type of numbers

Integer

int8, int16, int32, int64: integers in 8,16,32,64

bits)

uint8, uint16, uint32,uint64: unsigned integers

Non-integer

single: single-precision numbers

Double: double-precision numbers


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Logical expression

Evaluate the correctness of the statement

TRUE

FALSE

Six relationship operator1. == equal

2. ~= not equal

3. > greater than

4. >= greater than or equal to

5. < less than

6.


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Logical operator and values

logical operators

~: not

&: and

|: or

Logical value

1 (true)

0 (true)

10


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Logical operator precedence

Precedence (from the first to the last)

Parenthesis ()

Arithmetic operators

Relationship operators

==,~=,>,>=,


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The one-line if statement

ifcondition

statement

end

condition is usually a logical expression

Ifcondition is true, statementis executed, but if

condition is false, nothing happens.

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More on conditional statemet

ifcondition

statementA

else

statementB

end

condition is usually a logical expression

Ifcondition is true, statementA is executed, but ifcondition is false, statementB is executed.

Dont forget end, or MATLAB will wait forever.

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elseifladder

ifcondition1

statementsA

elseifcondition2

statementsBelseifcondition3

statementsC

else

statementsE

end

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Vector

Vector

Also called list, arrays in other language

Row vector

[1,2,3,4]

A vector can also be generated (initialized)

with the colon operator

J:m:k


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How to access items in vector

Subscript

x(k): k-th element of vector x

A subscript is indicated inside roundbrackets

(also called parentheses).

A subscript may be a scalar or a vector.

x(j:k): the vector of j-th, (j+1)-th, , k-th elements of

vector x

In MATLAB subscripts always start at 1.


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Creating matrix

Creating matrix use a semicolon to indicate the end of a row

e.g. >> a = [1,2,3; 4, 5,6]

a =

1 2 34 5 6

Individual elements of a matrix are referenced withtwo subscripts, the first for the row, and the second for

the column e.g. >> a(1,2)

Alternatively, you may use a single index by think amatrix as being unwounded column by column


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Some useful functions for matrix

operations

size

transpose using

reshape diag

find


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Matrix arithmetic operations

Some operations are not element-wise

Multiplication

Exponential

Some operations are element-wise

Addtion

Subtraction

Using . to specify the element-wise operations

Keeping the dimension of matrices consistent


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The keyword end in subscripts.

The keyword end refers to the lastrow or

column of an array.

There is a group of functions to generate

elementary matrices

eye, zeros, ones


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for struct

The for struct

forindex=j:k

statements

End

or

forindex=j:m:k

statements

end


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While struct

while struct

while condition

statements

end The while construct repeats statements WHILE its

condition remains true

The condition is tested each time BEFORE

statements are repeated. condition must depend on statements in some

way, otherwise the loop will never end.


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Finishing loops earlier before its end

using break

break struct

while condition for i = j:k,

statementsA statementsA

if (condionB), break; end; if (conditionB), break;end;statementsB statementsB

end end

During each repetition, after statemensA isexecuted, if conditionB holds true, the whileloops will end immediately and go to the next lineafter the loop.


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Execute part of statements during the

loops using continue

continue structwhile condition for i = j:k,

statementsA statementsA

if (condionB), continue;end; if (conditionB) continue;endstatementsB statementsB

end end

At each repetition, after statementsA is executed, if

conditionB holds true, statementsB will not beexecuted and the program will start the nextrepetition.


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function

A function M-file name.m has the following

general form:

function [ outarg1, outarg2, ] = name(

inarg1, inarg2, )

...

outarg1 = ... ;

Outarg2= ;


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More on rules of function

Keyword function

Input and output arguments.

Function names must follow the MATLAB rulesfor variable names.

Any variables defined inside a function are

local, inaccessible outside the function.

Recursive function


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data file by load and save

save myData A

save variable A into file mydata.mat

A = load(myData.txt)Import text (ASCII) data to A


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character

A-Z

a-z

0-9 Symbols: #,@,& and etc

Notation ofchar

enclosing the character in singlequotation marks

e.g. z

char


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Definition: a vector of chars

string

enclosing a sequence of letters in single quotation

marks

Apostrophe '

Double apostrophe: ''

Blank character

Enclosing a blank in single quotation marks: ' '

String


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Cell & Structure

Cell

Most general data object in Matlab

Enclosing the content by curly brackets

Structure

field

data container store one type of data

Using dot to separate structure name and field

name


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Graphics

plot

plot3

mesh

surf


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Efficient programming

Space pre-allocation

Vecterization to avoid loops find

Min

max sum,

cumsum,

prod,

cumprod

sort Diff

Deleting Sub-matrices with [ ]


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Image processing

imread

imwrite

Binary image

Greyscale image

Color image

Indexed color image

cz1102 computing & problem solving lecture 12

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