Lecture 1: Hello, MATLAB!

Transcription

1 Lecture 1: Hello, MATLAB! Math 98, Spring 2018 Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 1 / 21

2 Syllabus Instructor: Eric Hallman Class Website: Login:!cmfmath98 Password: See website for 1 Textbooks 2 Lecture schedule 3 Homework 4 Links to MATLAB documentation 1 Language fundamentals: language-fundamentals.html 2 Programming Scripts and Functions programming-and-data-types.html Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 2 / 21

3 Getting Started with MATLAB Obligatory first program: >> disp("hello, world!") Hello, world! Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 3 / 21

4 Getting started with MATLAB Matlab has five features: 1 Current Folder shows the files that MATLAB is accessing. By default MATLAB cannot execute files contained in other folders. 2 Command Window is what we just used to say Hello, world!. Here we can define variables, perform calculations, and much more. 3 Workspace is a MAT-file containing the variables you have defined in your session. 4 Editor allows us to save collections of commands as M-files. 5 Command History can be accessed using the up arrow. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 4 / 21

5 Current Folder pwd prints the current working directory dir lists its contents cd DIR-NAME can change the directory cd.. (double dots) moves up one level You can also do this by clicking the buttons over Current Folder. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 5 / 21

6 Command Window Among other things, it s a giant calculator. Operations: +,,, /,ˆ, exp( ),, log( ) 2 3 (1 + 2)/2 = log(4) = , log2(4) = 2, log10(4) =.6021 pi= , pi 4 2 = Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 6 / 21

7 Variables The workspace shows variables that have been defined in the current session. In particular, ans is by default the value of the last arithmetic computation we made. We can check the value of a variable by entering its name in the command window. >> ans ans = Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 7 / 21

8 Variables We can define our own variables, too! Variable names must start with a letter and can contain letters, digits, and underscores. MATLAB is case sensitive but all built-in MATLAB functions use lowercase letters, so if you use at least one capital letter in your variable names you can be sure to avoid any name conflicts. >> x1 = >> my variable = "howdy" >> frodobaggins33 = sqrt(2)*pi >> radius = 4 >> pi*radius^2 ans = Do your best to choose informative names for your variables. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 8 / 21

9 Variables Use a semicolon to suppress the output of a command. Using disp will suppress the ans = text, but will also not save the output to ans. Multiple commands can be placed on a line separated by semicolons. >> x = 5; y = 6; disp(x+y) 11 Use SHIFT-ENTER to start a new line. Use ellipses (...) and SHIFT-ENTER to continue a line. >> sqrt( ) ans = 5 Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 9 / 21

10 Variables Use clear to clear all variables from the workspace. Use clear VAR1 VAR2 to clear specific variables VAR1 and VAR2. >> x = 5; clear x; >> x Undefined function or variable x. Use clc to clear the command line. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 10 / 21

11 Editor Okay, it s finally time to make a proper script! In the command line, enter >> edit Hello.m An m-file is a file containing a script for MATLAB a sequence of instructions for the computer. The name of the file must have the format filename.m. For MATLAB to execute the file, it must be saved in the Current Directory. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 11 / 21

12 input A string is a sequence of characters enclosed by single or double quotations, e.g. teststring123x. The command input will prompt the user to input a number or string. If the input should be a string, then use input( instructions for input:, s ) Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 12 / 21

13 fprintf The command fprintf is used to display formatted strings that incorporate specified values. >> T = ; P = ; >> fprintf( Temperature = %6.2f, Pressure = %5.3e\n, T, P) Temperature = , Pressure = 1.215e+02 >> The formats are %d for integer, %e for scientific notation, and %f for floating point format. %s is used to include strings (rather than numbers), and the character \n adds a new line to the end of the output. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 13 / 21

14 Commenting with % Except within a string, everything following % is a comment. Comments do not get executed when the program runs, but can make the code easier to read by providing information about its organization and usage. Comments in the beginning lines of a program will be revealed when using the command help: >> help hello It s a program that says hello. help (as well as doc) is also invaluable when learning how to use various MATLAB functions. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 14 / 21

15 Exercise 1 A temperature can be converted from Fahrenheit to Celsius using the formula c = (5/9)(f 32), where c is Celsius and f is Fahrenheit. Write a script that prompts the user for a temperature in Fahrenheit, converts it to Celsius, and prints it in a nice format. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 15 / 21

16 Problem A quadratic polynomial has the form f (x) = x 2 + bx + c. We would like to know whether it has any roots in the interval [L, R]. We want to write a program that does the following: 1 prompts the user for real numbers b and c 2 prompts the user for real numbers L and R 3 determine whether the polynomial f (x) has any real roots at all if it does, determine whether it has any roots in [L, R] if not, say so In order to write this program, we will need a few more tools. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 16 / 21

17 Relations The following statements will take value 0 (if false) or 1 (if true) a < b: a less than b a > b: a greater than b a <= b: a less than or equal to b a >= b: a greater than or equal to b a == b: a equal to b (note the doubled equals sign!) a = b: a not equal to b Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 17 / 21

18 Logical Statements and(a,b) or equivalently a & b or(a,b) or equivalently a b not(a) xor(a,b) What do the commands && and do? Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 18 / 21

19 Boolean Expressions A boolean expression is any expression involving relations or logical statements: ((4 <= 100) ( 2 > 5))&(true false) Boolean expressions evaluate to 1 for true and 0 for false. Note that 0 and 1 are just numbers and are not in a separate class for logicals. >> 5 + true ans = 6 The order of operations is as follows: 1 negation 2 relations 3 and 4 or Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 19 / 21

20 if-else This construct is used where the decision to execute one or another set of computations depends on the value of a boolean expression. if this boolean expression is true execute these commands elseif this second expression is true instead then exectue these other commands else do this if those earlier conditions are false end Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 20 / 21

21 Exercise 2 Write a script that prompts the user for two numbers (call them x and y). Write a script that outputs The numbers are equal if x = y and The numbers are not equal otherwise. Math 98, Spring 2018 Lecture 1: Hello, MATLAB! 21 / 21