Introduction to Matlab Creating Matlab Scripts Birth Year

Introduction to Matlab

Creating Matlab Scripts

Birth Year Program • Get the user’s age as input • Display the user’s birth year • Use input() to get the age • Use disp to display the year

Type in Your Program

Give Your Script a Name

Run Your Program

Program in Action

Search Path

Improve the Birth Year Program • The call : “datestr(date, 10)” returns the current year in string format. • Rather than the line: “ 2003 – age”, we could have done: • current. Year. Str = datestr(date, 10); • current. Year = str 2 num(current. Year. Str); • birth. Year = current. Year – age;

Number guessing program Sample run : Please pick a number between 10 and 99 Now add the two digits of your number Substract the result from your number and enter the result: 36 Now subtract 4 from your number and enter the result: 42 The number you picked was 46

Number Guessing Program % Finds out the two digit number the user is thinking of disp('Please pick a number between 10 and 99'); disp('Now add the two digits of your number'); nine. A = input('Substract the result from your number and enter the result: '); A = nine. A / 9; nine. Aone. B = input(['Now subtract ' num 2 str(A). . . ' from your number and enter the result: ']); B=nine. Aone. B - 9 * A; disp(['The number you picked was ' num 2 str(10*A+B) ]); disp(['In other words, it was ' num 2 str(A) num 2 str(B) ]);

Computing Digits • Given a number and digit number, display the value of that digit. • Sample run: Please enter a number 56789 Which digit do you want ? 2 Your digit is : 8

Computing Digits % Gets a number from user and a digit no. starting with 1 % and returns the numeric value of that digit n=input('Please enter a number '); k=input('Which digit do you want ? '); ten. To. K = 10^k; first. K=rem(n, ten. To. K); K=floor(first. K/ (ten. To. K/10)); disp(['Your digit is : ' num 2 str(K)]);

Getting String Input >> str = input('Enter a string: >', 's'); Enter a string: >so were the days of fall >> disp(['The length of your string was : ' num 2 str(length(str)) ' characters. . . ']); The length of your string was : 24 characters. . . >> str = input('Enter a string: >'); Enter a string: >having said all that, ? ? ? having said all that, Error: Missing operator, comma, or semicolon. >> s = 'abcde'; >> s(1) ans =a >> s(2) ans =b

Computing Digits, String Version strn=input('Please enter a number ', 's'); k=input('Which digit do you want ? '); location = length(strn) - k + 1; disp(['Your digit is : ' strn(location)]);

A better guessing program • Sample run Multiply your shoe size with 5 and press enter. . . Now add 50, press enter when ready. . . Now multiply the result with 20 an then add 1003. . . Subtract your birth year from the final result and enter the value >5030 Your shoe size is : 50 Your age is : 30

A better guessing program input('Multiply your shoe size with 5 and press enter. . . '); input('Now add 50, press enter when ready. . . '); input('Now multiply the result with 20 an then add 1003. . . '); size. Age = input('Subtract your birth year from the final result and enter the value >'); size = floor(size. Age/100); age=rem(size. Age, 100); disp(['Your shoe size is : ' num 2 str(size) ]); disp(['Your age is : ' num 2 str(age) ]);

Some Other Problems • Decide which letter grade a student should receive based on his overall grade • Compute the tax of a sale item based on its type (food 5%, electronics 17%, …) • Diagnose a patient …

Algorithms • Systematic procedure that produces—in a finite number of steps— the answer to a question or the solution of a problem. The name derives from the Latin translation, Algoritmi de numero Indorum, of the 9 th-century Muslim mathematician al-Khwarizmi's arithmetic treatise “Al-Khwarizmi Concerning the Hindu Art of Reckoning. ” (Brittanica) • A computable set of steps to achieve a desired result. . . The word comes from the Persian author Abu Ja'far Mohammed ibn Mûsâ al. Khowârizmî who wrote a book with arithmetic rules dating from about 825 A. D. (NIST) • An algorithm is a sequence of finite number of steps arranged in a specific logical order which, when executed, will produce a correct solution for a specific problem.

Algorithm Representations – Flow Charts – Pseudo-code • Pseudo-code is a semi-formal, English-like language with a limited vocabulary that can be used to design and describe algorithms. • The main purpose of a pseudo-code is to define the procedural logic of an algorithm in a simple, easy-to-understand manner for its readers, who may or may not be proficient in computer programming.

Another Definition for Pseudocode • Pseudocode (pronounced SOO-doh-kohd) is a detailed yet readable description of what a computer program or algorithm must do, expressed in a formallystyled natural language rather than in a programming language. Pseudocode is sometimes used as a detailed step in the process of developing a program. It allows designers or lead programmers to express the design in great detail and provides programmers a detailed template for the next step of writing code in a specific programming language. • Because pseudocode is detailed yet readable, it can be inspected by the team of designers and programmers as a way to ensure that actual programming is likely to match design specifications. Catching errors at the pseudocode stage is less costly than catching them later in the development process. Once the pseudocode is accepted, it is rewritten using the vocabulary and syntax of a programming language. Pseudocode is sometimes used in conjunction with computer-aided software engineering-based methodologies. • It is possible to write programs that will convert a given pseudocode language into a given programming language.

Algorithm Example: How to drink a glass of milk 1. 2. 3. 4. 5. Enter kitchen Get Glass Get milk from fridge Fill glass with milk Drink it!

Expand 1 & 3 1. 1. 1 1. 2 1. 3 2. 3. 3. 1 3. 2 3. 3 4. 5. Enter kitchen walk to the kitchen door go through door <--walk into kitchen Get Glass Get milk from fridge open fridge get milk close fridge Fill glass with milk Drink it! door may be closed !

What if door is already open ! 1. 1. 1 1. 2 1. 3 2. 3. 3. 1 3. 2 3. 3 4. 5. Enter kitchen walk to the kitchen door open door and go through it walk into kitchen Get Glass Get milk from fridge open fridge get milk close fridge Fill glass with milk Drink it!

Final Algorithm 1. 1. 1 1. 2. T 1. 3 2. 3. 3. 1 3. 2 3. 3 4. 4. 1. 1 5. Enter kitchen walk to the kitchen door if door is closed then open it walk into kitchen Get Glass Get milk from fridge open fridge get milk close fridge Fill glass with milk while glass not full pour some milk into it Drink it!

If Statement: Single Option Pseudo-code : if (condition) statement 1 statement 2 condition evaluated true … false Matlab: statements if (condition) statement 1 statement 2 … end

If statement: two options Matlab: if (condition) true condition evaluated statement. T 1 false statement. T 2 … statement. T statement. F else statement. F 1 statement. F 2 … end

Doctor’s Algorithm check patient’s temperature Yes Is temp. < 36? Yes Put on a sweater No Is temp. > 39? Take an aspirin No Go home!

Doctor with Nested If-else Pseudo-code: Matlab Way: if (temp < 36) put on a sweater else if (temp > 39) take an aspirin else go home end

Doctor with If-else & else if Pseudo-code: Matlab Way: if (temp < 36) put on a sweater else if (temp > 39) take an aspirin else go home if (temp < 36) put on a sweater elseif (temp > 39) take an aspirin else go home end

Absolute Value Example get value from user • Get value from user • If the value is negative – Negate the value • Display the value if value negative true negate value display value false

Absolute Value Program value=input('Enter a number : >'); if (value < 0) value = -value; end disp(['The absolute value of your number is ' … num 2 str(value) ]);

Absolute Value for Complex Numbers • get value from user • if value is real – abs. Value = usual absolute of value • else if real part of value is zero – abs. Value is usual absolute of imaginary part of value • else – abs. Value is square root of sum of squares of real and imaginary parts of value • Display abs. Value as the result

Complex Absolute in More Detail • get value from user • if value is real – if value is negative • abs. Value is negative of value – else • abs. Value = value • else if real part of value is zero – abs. Value = imaginary component of value – if (abs. Value < 0) • abs. Value = -abs. Value • else – abs. Value is square root of sum of squares of real and imaginary parts of value • Display abs. Value as the result

Some Remarks • Note that we had a lot of flexibility in expressing same things: “if value is negative” , “if (value < 0)”; “=“ , “is”, “assigned to”… • Usually you should follow consistent wording, but you are flexible as long as what you express is clear (unambiguous) • Note tat we had flexibility in first 2 parts of the if statement as well. • Indentation is crucial in pseudo-code

Without Indentation get value from user if value is real if value is negative abs. Value is negative of value else abs. Value = value else if real part of value is zero abs. Value = value if (abs. Value < 0) abs. Value = -abs. Value else abs. Value is square root of sum of squares of real and imaginary parts of value Display abs. Value as the result

Matlab Program value=input('Enter a number : >'); abs. Value=0; if (isreal(value)) % or if imag(value) == 0 if (value < 0) abs. Value = -value; else abs. Value = value; end elseif (real(value) == 0) abs. Value=imag(value); if (abs. Value < 0) abs. Value = -abs. Value; end else abs. Value = sqrt(real(value)^2 + imag(value)^2); end disp(['The absolute value of your number is ' num 2 str(abs. Value) ]);

Matlab Program …

Testing… Enter a number : >3 The absolute value of your number is 3 >> absolute_complex Enter a number : >-3 The absolute value of your number is 3 >> absolute_complex Enter a number : >3 i The absolute value of your number is 3 >> absolute_complex Enter a number : >-3 i The absolute value of your number is 3 >> absolute_complex Enter a number : >3+4 i The absolute value of your number is 5 >> absolute_complex Enter a number : >3 -4 i The absolute value of your number is 5 >> absolute_complex Enter a number : >-3 -4 i The absolute value of your number is 5

Algorithm Example Give an algorithm for deciding what to play. Rules are as follows: • play golf if sky is clear and temp. < 35 • If it is raining but there is no lightining and temp. < 15 play soccer, otherwise play an indoor game. • If it is cloudy, go running • if sky is clear but temp > 35 stay at home • Go indoor swimming if it is raining and temp > 15 • play ping pong when other indoor activities are not suitable

One Solution. .

Pseudo-code version If raining if temp > 15 go indoor swimming (raining & temp > 15) else if no lightining play soccer (raining & temp < 15 & no lightining) else play ping pong (raning & temp < 15 & lightining) else if cloudy go running else if temp < 35 play golf else stay at home

What Goes Inside the If() ? • • Any real value any non-zero value is interpreted as “true” zero value represents “false” can also use functions : “true” and “false” if (123. 45) if (0) if (true)

What Produces a Logical Answer? • • Literals like 0, 5, true, false … Relational Operators like <, >. . Logic Operators like &&, || Functions like isreal(), ischar() …

Relational Operators Operator Description < Less than <= Less than or equal to > Greater than >= Greater than or equal to == Equal to ~= Not equal to

Logical Operators Inputs and or not xor A B A &&B A || B ~A xor(A, B) 0 0 1 0 1 1 1 1 1 0 0

Absolute Solution (tricky version) abs. Value=0; if (imag(value) == 0 || real(value) == 0) abs. Value=imag(value) + real(value); if (abs. Value < 0) abs. Value = -abs. Value; end else abs. Value = sqrt(real(value)^2 + imag(value)^2); end

Absolute Solution (better) abs. Value=0; if (imag(value) ~= 0 && real(value) ~= 0) abs. Value = sqrt(real(value)^2 + imag(value)^2); else if (imag(value) == 0) abs. Value = real(value); else % do not need to ask real(value) == 0 abs. Value = imag(value); end if (abs. Value < 0) abs. Value = -abs. Value; end

Doctor Algorithm Questions chained : Individual Questions: if (temp < 36) put on a sweater elseif (temp > 39) take an aspirin else go home end if (temp < 36) put on a sweater end if (temp > 39) take an aspirin end if (temp <= 39 && temp >= 36) go home end