CSE123 Lecture 3 Files and File ManagementScripts

Matlab provides a group of commands to manage user files pwd: Print working directory – displays the full path of the present working directory. cd path: Change to directory (folder) given by path, which can be either a relative or absolute path. dir : Display the names of the directories (folders) and files in the present working directory. what: Display the names of the M-files and MAT-files in the current directory. delete file: Delete file from current directory type file: Display contents of file (text file only, such as an M-file).

Saving and Restoring Matlab Information It is good engineering practice to keep records of calculations. These records can be used for several purposes, including: To revise the calculations at a later time. To prepare a report on the project. Diary Command The diary commands allows you to record all of the input and displayed output from a Matlab interactive workspace session. The commands include: diary file: Saves all text from the Matlab session, except for the prompts (>>), as text in file, written to the present working directory. If file is not specified, the information is written to the file named diary. diary off: Suspends diary operation. diary on: Turns diary operation back on. diary: Toggles diary state

Saving and Restoring Matlab Information Example: >> diary roots >> a=1; >> b=5; >> c=6; >> x = -b/(2*a); >> y = sqrt(b^2-4*a*c)/(2*a); >> s1 = x+y s1 = -2 >> s2 = x-y s2 = -3 The file roots is written in your current working directory. It can be displayed by Matlab command type roots.

Storing and Loading Workspace Values save : Stores workspace values (variable names, sizes, and values), in the binary file matlab.mat in the present working directory save data : Stores all workspace values in the file data.mat save data_1 x y :Stores only the variables x and y in the file data_1.mat load data_1 :Loads the values of the workspace values previously stored in the file data_1.mat

Script M-Files Group of Matlab commands placed in a text file with a text editor. Matlab can open and execute the commands exactly as if they were entered at the Matlab prompt. The term “script” indicates that Matlab reads from the “script” found in the file. Also called “M-files,” as the filenames must end with the extension ‘.m’, e.g. example1.m.

Script M-Files Example : Create the file named qroots.m in your present working directory using a text editor: %qroots:Quadratic root finding script format compact; a=1; b=5; c=6; x = -b/(2*a); y=sqrt(b^2-4*a*c)/(2*a); s1 = x+y s2 = x-y To execute the script M-file, simply type the name of the script file qroots at the Matlab prompt: >> qroots a = 1 b = 5 c = 43 6 s1 = -2 s2 = -3

Effective Use of Script Files 1. The name must begin with a letter and may include digits and the underscore character. 2. Do not give a script file the same name as a variable it computes 3. Do not give a script file the same name as a Matlab command or function. To check existence of command, type exist(’rqroot’). This command returns one of the following values: 0 if rqroot does not exist 1 if rqroot is a variable in the workspace 2 if rqroot is an M-file or a file of unknown type in the Matlab search path ….

Effective Use of Script Files 4. All variables created by a script file are defined as variables in the workspace. After script execution, you can type who or whos to display information about the names, data types and sizes of these variables. 5. You can use the type command to display an M-file without opening it with a text editor. For example, to view the file rqroot.m, the command is type rqroot.

Matlab Search Path, Path Management Matlab search path: Ordered list of directories that Matlab searches to find script and function M-files stored on disk. Commands to manage this search path: matlabpath: Display search path. addpath dir: Add directory dir to beginning of matlabpath. If you create a directory to store your script and function M-files, you will want to add this directory to the search path. rmpath dir: Remove directory dir from the matlabpath.

Different types of Variables Logical operators, Conditional Statements and If Blocks

 Complex. a + b i a and b are real numbers i is an imaginary number. ( i 2 = -1 ) Different types of Variables  Integer. positive whole numbers {1, 2, 3,... } negative whole numbers {-1, -2, -3,... } zero {0} Matlab Notation N= a+bi or N=a+bj Matlab Notation N= a+bi or N=a+bj  Real. real number. Matrix index (ex: B(2,1) ) Counters All calculus results… Complex calculus Geometry Vector calculus A= 5+10i; B= j; Examples: Numerical Variables

 Character/string. Strings of alphanumeric elements Different types of Variables Matlab Notation A=’string’ Matlab Notation A=’string’ All labels and titles. Filenames Strings and characters follow the same rules as other matrices, with each character counting for one element. >>myname=’James’; >>whos myname Name Size Bytes Class myname 1x5 10 char array Example: name=’ James’; Date=’October 7th’; Examples: Character/string Variables

Logical Variables  Logical Variables or Boolean. Logical expression with 2 states: 0 or 1 which means: false or true Condition statements Decision making >>A=true A = 1 >> whos A Name Size Bytes Class A 1x1 1 logical array Example: >>B=false B = 0 >> whos B Name Size Bytes Class B 1x1 1 logical array Example: Different types of Variables

Structured Programming Initialization Calculation Results Input Initialization Sequential Programming Structured Programming Input Calculation Calculation 1Calculation 2 Initialization Result 1Result 2 ? Decision making Condition statements

Relational Operators  Decision making uses comparison of logical variables  Comparison is done by creating logical expressions Format of SIMPLE Logical Expressions: ****** expression1 relational-operator expression2****** relational- operator Comparison ==Is equal to >Is greater than <Is smaller than >=Is greater or equal to <=Is smaller or equal to ~=Is not equal to >> A=1; B=2; >> A==B Example: ans = 0 >> A>B ans = 0 >> A<B ans = 1 >> A>=B ans = 0 >> A<=B ans = 1 >> A~=B ans = 1

Logical Operators Format of COMPOUND Logical Expressions: (exp1 relational-op exp2) Logical operator (exp3 relational-op exp4) Logical operator operation &and |or xoror (exclusive) ~not ABC= A&B ABC= A|B AB C= xor(A,B) Truth Table ~(A&B) ~xor(A,B) ~(A|B)

Logical Variables >> A=1; B=2; >> (A==B) & (A>B) Examples: >> (A<B) & (A==B) ans = 0 >> (A==B) | (A>B)ans = 0 >> (A<B) | (A==B) ans = 1 >> xor( (A==B), (A<B) ) ans = 1 >> ~(A<B) ans = 0 >> xor( (A~=B), (A<B) ) >> ~(A>B) ans = 1 ans = 0 >> (A>0) & (B>A)ans = 1 >> (A>0) & (B>A)&(B<0) ans = 0

Structured Programming Format of if statement: if Logical Expression Statements …… end if True False Statement Format of if else statement: if Logical Expression Statement 1 else Statement 2 end if True False Statement1Statement2

Example: iftest1.m % Program to test the if statement #1 X=input(‘Enter value for x:’); if X>=0 Y=sqrt(X); fprintf(‘The squareroot of %3.2f is %4.3f’,X,Y) end % Program to test the if statement #1 X=input(‘Enter value for x:’); if X>=0 Y=sqrt(X); fprintf(‘The squareroot of %3.2f is %4.3f’,X,Y) end >>iftest1 Enter value for x: 9 The squareroot of 9.00 is >>iftest1 Enter value for x: 9 The squareroot of 9.00 is Input X Calculate If X>=0 Initialization Display Result End of script True False >>iftest1 Enter value for x: -2 >> Structured Programming

Example: iftest2.m % Program to test the if statement #2 X=input(‘Enter value for x:’); if X>=0 Y=sqrt(X); fprintf(‘The squareroot of %3.2f is %3.4f’,X,Y) else disp(‘x is negative: there is no real result’) end % Program to test the if statement #2 X=input(‘Enter value for x:’); if X>=0 Y=sqrt(X); fprintf(‘The squareroot of %3.2f is %3.4f’,X,Y) else disp(‘x is negative: there is no real result’) end >>iftest2 Enter value for x: 3 The squareroot of 9.00 is >>iftest2 Enter value for x: -2 x is negative: there is no real result >> >>iftest2 Enter value for x: 3 The squareroot of 9.00 is >>iftest2 Enter value for x: -2 x is negative: there is no real result >> Input X Calculate If X>=0 Initialization Display Result End of script True False Display NO Result Structured Programming

Format of if elseif else statement: if Logical Expression Statements 1 elseif Logical Expression Statements 2 else Statements 3 end if False Statement1 elseif Statement2 Statement3 True False True Structured Programming

Example: iftest3.m % Program to test the if statement #3 X=input(‘Enter value for x:’); if X>0 disp(‘x is positive’); elseif X<0 disp(‘x is negative’); else disp(‘x equal 0’); end % Program to test the if statement #3 X=input(‘Enter value for x:’); if X>0 disp(‘x is positive’); elseif X<0 disp(‘x is negative’); else disp(‘x equal 0’); end >>iftest3 Enter value for x: 3 x is positive >>iftest3 Enter value for x: -2 x is negative >>iftest3 Enter value for x: 3 x is positive >>iftest3 Enter value for x: -2 x is negative Input X If X>0 Initialization End of script True False Display Result >0 Display Result <0 If X<0 Display Result = 0 True False Structured Programming

Problem: Pick a random number N (-2<N<2) Calculate B= “nesting “ If N positive calculate: A=log(N) if A positive calculate: B=sqrt(A) % nested “if statements” example N= rand(1)*4-2; if N>=0 A=log(N); if A>0 B=sqrt(A); end % nested “if statements” example N= rand(1)*4-2; if N>=0 A=log(N); if A>0 B=sqrt(A); end % nested “if statements” example N= rand(1)*4-2; if N>=0 A=log(N); if A>0 B=sqrt(A); end % nested “if statements” example N= rand(1)*4-2; if N>=0 A=log(N); if A>0 B=sqrt(A); end Use indentation (Tab key) Structured Programming

The “ SWITCH” structure switch variable case test1 Statement 1 case test2 Statement 2 ….. otherwise Statement n end Statement3 Switch Statement nStatement1 Statement4Statement2 Structured Programming

The “ SWITCH” structure % program to test switch A=input('Your choice [1,2 3] ? '); switch A case 1 disp('Choice 1') case 2 disp('Choice 2') case 3 disp('Choice 3') otherwise disp('Wrong choice') end % program to test switch A=input('Your choice [1,2 3] ? '); switch A case 1 disp('Choice 1') case 2 disp('Choice 2') case 3 disp('Choice 3') otherwise disp('Wrong choice') end >> Testswitch Your choice [1,2 3] ? 1 Choice 1 >> Testswitch Your choice [1,2 3] ? 7 Wrong choice >> Testswitch Your choice [1,2 3] ? 2 Choice 2 >> Testswitch Your choice [1,2 3] ? 3 Choice 3

Example1 Write a script example.m to find roots of a second order equation ax 2 +bx+c=0. When the script is executed it will –ask the user enter the coefficients a,b,c –calculate discriminant –calculate the roots and display the case according to sign of discriminant.

Example2 Write a script that allows a user to enter a string containing a day of a week (“Sunday”, “Monday” etc) uses a switch construct to convert the day to its corresponding number, where Monday is the first day of the week. Print out the resulting day number. Also be sure to handle the case of an illegal day name.