Script and Function File

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1 INC151 Electrical Engineering Software Practice Script and Function File Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 1

Script Files MATLAB script file (Called an M-file) is a text file that contains one or more MATLAB commands and, optionally, comments. The file is saved with the extension ".m i.e. xxx.m. When the filename i.

2 Script Files MATLAB script file (Called an M-file) is a text file that contains one or more MATLAB commands and, optionally, comments. The file is saved with the extension ".m i.e. xxx.m. When the filename i.e. xxx (without the extension) is issued as a command in MATLAB, the file is opened, read, and the commands are executed as if input from the keyboard. The result is similar to running a program in C. Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 2

3 Script vs Function Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 3

4 Creating M-file Script file Function file Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 4

5 Creating M-file MATLAB Editor/Debugger Window Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 5

6 Creating M-file Comment Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 6

$Save the file created as test.m in MATLAB working directory: i.e. C:\MATLAB\R2009a\ To add/set path go to the$ menu File/Set Path In MATLAB command window, type the M-file name (without its extension) >>test Alternatively,

menu File/Set Path In MATLAB command window, type the M-file name (without its extension) >>test Alternatively,

7 Calling M-file Save the file created as test.m in MATLAB working directory: i.e. C:\MATLAB\R2009a\ To add/set path go to the menu File/Set Path In MATLAB command window, type the M-file name (without its extension) >>test Alternatively, use Run icon in the Editor window The comments at the beginning of the M-file will appear when user type help M-file name. >>help test Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 7

8 M-file Functions Functions are program routines, usually implemented in M- files, that accept input arguments and return output arguments. They operate on variables within their own workspace. This workspace is separate from the workspace you access at the MATLAB command prompt. The syntax for a MATLAB function definition is: Function name function[return_val1,, return_valn] = myfunc(in1,,ink) where return_val1 through return_valn are the specified returned values from the function and in1 through ink are the values sent to the function. Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 8

9 Creating M-file functions Create the first M-file function shown below and save it as myfunc.m Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 9

10 Using M-file Functions In order to use the function properly, it is worth to check what the function is used for and what are inputs required and returned output? >>help function name %i.e. help roots, help sqrt >>help myfunc % good function should have % the function explanation To use the function, type the function name following with the inputs required >>myfunc(3,4) >>myfunc(1,1) Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 10

>>x=myfunc(3,4) % or [x]=myfunc(3,4) return output to x Dr.

11 Returning Variable In previous example, there are no return variables. To return variables, use following case. >>x=myfunc(3,4) % or [x]=myfunc(3,4) return output to x Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 11

12 Script and Function Alternatively, normal script file can do the same job. >>myfile1 %call m-file Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 12

13 Frequently Used Commands input:request user input i.e. user_entry = input('prompt'); disp(var):display text or array,without printing the variable name Echo:The echo command controls the echoing of M- files during execution. This uses for debugging echo on:turns on the echoing of commands in M-files echo off:turns off the echoing of commands in M-files Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 13

14 Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 14

$2345; Digits to the right of the decimal point Field width Control Code fprintf('the answer is %3.1f \n',a) Format Argument Variable Relace format specifier with %1.3f,%12f,%d,%g,%e Dr.$

15 fprintf fprintf: The fprintf function sends information (the arguments) according to the specified format to the file. Example A=1.2345; Digits to the right of the decimal point Field width Control Code fprintf('the answer is %3.1f \n',a) Format Argument Variable Relace format specifier with %1.3f,%12f,%d,%g,%e Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 15

16 fprintf Format specifier Control codes: \n,\r,\t,\b,\f can be used to produce linefeed(new line),carriage return, tab, backspace, and formfeed characters respectively. Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 16

The function accepts a single input argument(vector x) and returns a single output

17 Exercise 1 Create the M-file function named average.m to calculate the average(mean) of the elements in the input vector x [x1 x2 x3 xn]. The function accepts a single input argument(vector x) and returns a single output argument(average value). [15 mins] Example >>x=[ ]; >>y=average(x) >>average is 3 y= 3 Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 17

Homework Write a function to calculate 1. magnitude and 2.phase (in degree) of the input (complex number only) z=x+yi. Also calculate 3. x+y. Example. >>z=3+4i >>myfile(z) mag=5.

18 Homework Write a function to calculate 1. magnitude and 2.phase (in degree) of the input (complex number only) z=x+yi. Also calculate 3. x+y. Example. >>z=3+4i >>myfile(z) mag=5.00 phase=53.13 degree x+y=7.00 Hint Try fprintf command which is considered better than disp command Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 18

19 End Dr.Wanchak Lenwari :Control System and Instrumentation Engineering, KMUTT 19

MATLAB - Lecture # 4

MATLAB - Lecture # 4 Script Files / Chapter 4 Topics Covered: 1. Script files. SCRIPT FILE 77-78! A script file is a sequence of MATLAB commands, called a program.! When a file runs, MATLAB executes the