MATLAB Cheat Sheet: Data Types, Arrays, Operators, Functions, and Programming Basics, Study notes of Printing

Download MATLAB Cheat Sheet: Data Types, Arrays, Operators, Functions, and Programming Basics and more Study notes Printing in PDF only on Docsity! MATLAB Cheat Sheet Miscellaneous useful notes 1. Text after a percent sign (%) represent comments, and are ignored by the code. 2. Text in parentheses is evaluated by MATLAB prior to other text, in a manner identically to how parentheses are treated in math. 3. The two basic windows in MATLAB for the user to work in are the Command Window and the Editor. The Command Window is for quick commands that the user wishes to see executed; it acts out one line of code at a time, and prints the result unless that result is suppressed by the user. The Editor is for writing larger pieces of code in the form of functions or scripts, both of which are described toward the end of this document. 4. To suppress printing of command output, a simicolon (;) can be placed after the command. E.g., x=4 will assign the value 4 to x, and print x=4 to the screen. x=4; will assign the value 4 to x, without printing x=4 to the screen. 5. To clear variable assignments, type clear nameOfVariable. E.g., clear x will make it so that x no longer has any assigned value. To do this for all variables, type clear all. Data types The most important data types in MATLAB are doubles, strings, and Booleans; these are MATLAB's default numeric, text, and logical data types. Below, examples of each of these are given - doub1 and doub2 are doubles, str1 and str2 are strings, and boo1 and boo2 are Booleans. doub1=3.0;doub2=1; str1='hello';str2='h'; boo1=false;boo2=5>2; Arrays An array is a list of data types. It can be multidimensional, though MATLAB works most easily with 1- and 2-dimensional arrays. Arrays can be dened with in several ways. Below, r1 and r2 each represent a single-row array - r1 is dened explicitly, and r2 is dened with a handy MATLAB notation. c1 and c2 are similarly dened single-column arrays. M1 is a 2-dimensional array. r1=[1,2,3,4,5]%Commas to separate entries in an array within a row. r2=1:2:9%This is equivalent to writing r2=[1,3,5,7,9]. The notation is start:step:stop. %A notation start:stop can also be used, which simply means start:1:stop. c1=[1;2;3;4;5]%semicolons to separate rows. c2=(1:2:9)'%The ' symbol means "transpose", i.e., switch the role of rows and columns. M1=[1,2,3;4,5,6;7,8,9]%M1 is a 2-dimensional array. To select an element of an array, the format is ArrayName(index) for a 1D array, and ArrayName(rowIndex,colIndex) for a 2D array. The lowest array index in MATLAB arrays is the number 1. r2(2)%Gives 3, since the second entry in r2 is 3. c2(4)%Gives 7, since the fourth entry in r2 is 3. M1(3,2)%Gives 8, since M1(3) is [7,8,9] and [7,8,9](2) is 8. Finally, arrays can be concatenated, which means added onto. In the other direction, subarrays of a given array can be selected. There are variations on both of these operations, but the most basic form of each is demonstrated below - more detail can be found online. rbig=cat(2,r1,r2)%cat(2,array1,array2) concatenates array1 and array2 row-wise. %This gives rbig=[1,2,3,4,5,1,3,5,7,9]. cbig=cat(1,c1,c2)%cat(1,array1,array2) concatenates the two specified arrays column-wise. %This gives cbig=[1;2;3;4;5;1;3;5;7;9]. r2small=r2(2:4)%r2small=[3,5,7]. 1 Operators MATLAB's basic arithmetic operators are addition (+), subtraction (-), multiplication (*), division (/), and exponentiation (^), and modulo (mod(a,b)). These are used to combine several numbers or arrays to get a new number or array. By default, these operations act on arrays as they would act on matrices for matrix multiplication. This does not matter for addition, subtraction, or modulo, but does matter for the others. To perform the same operation element-wise, put a dot in front of the operation (.*, ./, .^). Examples are demonstrated below. 2+3%outputs 5. 2*3%outputs 6. r1+r1%outputs [2,4,6,8,10]. r1*r1%outputs error, since dimensions aren't consistent for matrix multiplication. r1.*r1%outputs [1,4,9,16,25] by element-wise multiplication. r1*c1%outputs 55, since the matrix multiplication gives 1*1+2*2+3*3+4*4+5*5=55 c1*r1%outputs [1,2,3,4,5;2,4,6,8,10;3,6,9,12,15;4,8,12,16,20;5,10,15,20,25], %since this is what the matrix multiplication gives. [1,1;1,1]^2%outputs [2,2;2,2] by matrix multiplication. [1,1;1,1].^2%outputs[1,1;1,1] by element-wise exponentiation. MATLAB's basic relational operators are equals (==), greater than (>), less than (<), greater than or equal to (>=), less than or equal to (<=), not equal ( =), and is equal( isequal(M1,M2)). All of these give a Boolean of true (1) or false (0) as they would evaluate to mathematically. The isequal() function is dened specically for arrays, and gives true if its array arguments are equal to one another. Examples are demonstrated below. 4==2*2%evaluates to true, since 4=2*2. 4==2*3%evaluates to false, since 2*3 does note equal 4. 4>2%evaluates to true, since 4 is greater than 2. 2<2%evaluates to false, since 2 is not less than itself. 2<=2%evaluates to true, since 2 is less than or equal to itself. 4~=2%evaluates to true, since 4 is not equal to 2. 2~=2%evaluates to false, since 2 is not not equal to itself. isequal(M1,M1)%evaluates to false, since M1 is the same array as itself. isequal(r1,r2)%evaluates to false, since these two arrays are different. MATLAB's basic logical operators are and (&), or (|), and not (~). & and | take two or more Booleans and output a new Boolean. ~ takes a single Boolean and outputs a new Boolean. They all play the same role as they do in language. Examples are demonstrated below. true&true%outputs true. true&false%outputs false. false&true%outputs false. false&false%outputs false. true|true%outputs true. true|false%outputs true. false|true%outputs true. false|false%outputs false. ~true%outputs false. ~false%outputs true. 2<2|4>2%outputs true, since this is the same as false|true. ~2<3%outputs false, since this is the same as ~true. (2<2|4>2)&(~2<3)%outputs false, since this is the same as true&false. Functions A function is anything that takes one or more data types as an input, and either performs a task based on that input, or gives one or more data types as an output. Some examples of functions already built into MATLAB are: sin(x) %takes x as an input and gives the sine of x as an output. isequal(x,y) %takes two doubles x and y as inputs and gives true or false as an output, %depending on whether they are equal. plot(x,y) %takes two arrays x and y as inputs and performs a task, namely, plots y against x. It is extremely useful to be able to create your own functions. To do so in MATLAB, you create a text le that is formatted in a way that MATLAB understands, and save it with the extension ".m" in a folder where MATLAB 2