EE 1105 Pre-lab 3 MATLAB - the ins and outs

Transcription

1 EE 1105 Pre-lab 3 MATLAB - the ins and outs INTRODUCTION MATLAB is a software tool used by engineers for wide variety of day to day tasks. MATLAB is available for UTEP s students via My Desktop. To access MATLAB, please refer to My Desktop tutorial. This lab will give an insight into the following topics: 1) Input/Output 2) Plotting 3) Example program with popular commands The best way to learn a programming language is through hands on work using examples. Practice the examples as you learn the commands in the command window of MATLAB as shown in Fig. 1. Figure 1. MATLAB default view Some Pointers: i. the syntax for using the command is highlighted ii. the command or program to be exactly typed in the command window has this kind of font

2 iii. if the explanation or example for a command is not clear enough, it is encouraged to type help commandname in the command window for more information iv. a semicolon ( ; ) at the end of a command is used to suppress the display of the variable in the command window v. to comment text in the program (for better understanding of the code), use % before the text, like % this is a comment 1. Input/Output Most of the electrical or electronic systems are designed to accept input and feedback the output. Similarly MATLAB provides routines/commands for user input and display the output. 1.1 Input There are 2 ways MATLAB accepts inputs from the user: input and menu commands. Only the input command is discussed here input command There are two ways the input command can be used: a) to accept a string/value b) to accept a text (string with spaces) For more information, type help input in the command window. (a) Syntax: variable = input (' string ') variable - input value is stored string - text that will prompt the user to type voltage = input ('What is the value of voltage in volts: ') resistance = input ('What is the value of the resistance in ohms: ') current = voltage / resistance (b) Syntax: variable = input (' text ', 's') variable - input value is stored string - text that will prompt the user to type myname = input ('Enter your full name: ', 's') 2

3 1.2 Output Getting a feedback of the program at intermediate stages is very important during programming. There are 2 ways to output information: disp and fprintf disp command Given that a variable is defined, once way of displaying the contained information is using this syntax: disp( variable ) The command can also be used to display text or string using: disp( 'string' ) voltage = input ('What is the value of voltage in volts: ') resistance = input ('What is the value of the resistance in ohms: ') current = voltage / resistance; disp( 'The current in amps using ohms law is: ') disp( current ) fprintf command This command is similar to disp, except there is more control over the formatting of the information to be displayed. The difference can be observed in the following example. voltage = input ('What is the value of voltage in volts: ') resistance = input ('What is the value of the resistance in ohms: ') current = voltage / resistance; fprintf( 'The current in amps using ohms law is: %f amps\n', current) It can be observed that the text is displayed along with the current value using the control character %f, which denotes a fixed point value. \n is added at the end of the displayed text to add a new line. myname = input ('Enter your full name: ', 's'); fprintf( 'My name is %s \n', myname ) Some of the commonly used control characters are listed below with examples. For more information type help fprintf in the command window. 3

4 Control character Use Example %s Inserts text fprintf('%s', textvariable) %f Inserts fixed point value fprintf('%f', Variable) %d Inserts integer value fprintf('%d', Variable) \n Inserts a new line fprintf('%f\n', Variable) 2. Plotting 2.1 Verifying Ohms Law The simplest way to plot a graph is to use plot command. The following example creates two arrays for voltage and current. The objective is to plot voltage versus current to check ohms law for a given resistor (1200 ohms). voltage = [ ]; current = [ ]; figure plot(voltage, current); % plot(xvariable, yvariable); xlabel ( 'voltage in volts' ) ylabel ( 'current in milli amps' ) title ( 'Resistor with 1200 ohms' ) Command to create a new graph window: figure Command to display name for the x-axis: xlabel ( 'string' ) Command to display name for the y-axis: ylabel ( 'string' ) Command to display name for the figure: title ( 'string' ) 2.2 subplot command Before the subplot command is discussed, let's look at creating an array between a given range. In the above example it is assumed that the voltage values will vary between 0 volts and 110 volts in increments of 10 volts. Instead of typing all the values, a more intelligent way can be used to create such an array: variable = startvalue : incrementvalue : stopvalue voltage = 0 : 10 : 110; current = [ ]; plot(voltage, current); % plot(xvariable, yvariable); xlabel ( 'voltage in volts' ) ylabel ( 'current in milli amps' ) title ( 'Resistor with 1200 ohms' ) Syntax for subplot: subplot ( numberofrows, numberofcolumns, figurenumber ) 4

5 Create a variable called time for x-axis. time = 0:0.1:10; figure create a figure, which can diplay 6 graphs in a 3 columns and 2 rows order. subplot(3,2,1) Use the function sin to calculate the sin(x) values. plot ( time, sin(time) ) title ( 'sin(x)' ) Repeat the subplot as seen above for 2sin(x), sin(2x), 2sin(2x), sin(x+π/2) and sin(x+π/2). subplot(3,2,2) plot ( time, 2*sin(time) ) title ( '2sin(x)' ) subplot(3,2,3) plot ( time, sin(2*time) ) title ( 'sin(2x)' ) subplot(3,2,4) plot ( time, 2*sin(2*time) ) title ( '2sin(2x)' ) subplot(3,2,5) plot ( time, sin(time + pi/2) ) title ( 'sin(x + pi/2)' ) subplot(3,2,6) plot ( time, sin(time - pi/2) ) title ( 'sin(x - pi/2)' ) Note: To copy the above generated graph to a word document, goto MATLAB figure -> Edit -> Copy Figure 5

6 goto word document -> Home -> Paste 3. Example program with popular commands The objective of this program is to familiarize with commonly used commands. The program is broken down in steps to give a detailed explanation. Either the command window or editor can be used for this task. To use editor, goto File -> New -> Blank M-File. In the editor window type all the commands and press F5 to run the program. The user is prompted to enter 10 numbers. The program should evaluate if exactly 10 or greater than 10 or less than 10 numbers are entered. If exactly 10 numbers are entered, then only calculate the maximum, minimum, mean, median, mode, standard deviation and sum of all the numbers. delete all the variables from the workspace clear all clear the command window clc Prompt the user to enter numbers in array format numbers = input('enter 10 numbers in array format like [1 2]= '); use if condition to check the count of the numbers to get the count of the numbers, use size command use > for greater than and < for less than condition if ( size(numbers) > 10 ) disp ( 'More than 10 numbers are entered' ) elseif ( size(numbers) < 10 ) disp ( 'Less than 10 numbers are entered' ) else disp ( 'Exactly 10 numbers are entered' ) fprintf ( 'Maximum value = %f \n', max(numbers) ) fprintf ( 'Minimum value = %f \n', min(numbers) ) fprintf ( 'Mean value = %f \n', mean(numbers) ) fprintf ( 'Median value = %f \n', median(numbers) ) fprintf ( 'Mode value = %f \n', mode(numbers) ) fprintf ( 'Standard deviation = %f \n', std(numbers) ) fprintf ( 'Sum = %f \n', sum(numbers) ) end Write a program that accepts a number from the user and evaluates the following function: 6

7 y = x2 + 2x + 5 x 3 clear all; clc; % Prompt the user to enter numbers in array format x = input ('Enter a number = '); % Calculate the numerator of the function numerator = ( x*x ) + ( 2*x ) + 5; % Calculate the denominator of the function % find y denominator = ( x*x*x ); y = numerator / denominator; % display the result in the command window PRELAB fprintf( 'y = %f \n', y ); For each question, give the code with output along with explanation. 1. For the following questions, z = 100/810. Write the MATLAB output that would result from each statement. a) >> disp(z) b) >> disp(the value of z is '), disp(z) c) >> fprintf('%f', z) d) >> fprintf('%g', z) e) >> fprintf('%e', z) f) >> fprintf('%e', z) 2. Plot the following functions on one figure using subplot command. Since there are 4 graphs to plot, use 2 columns and 2 rows format. The range for the time axis t is from 0 to 7 in increments of a) cos (t) b) cos (t + π/2) c) 3cos (2t) -2 d) cos (2t) +1 7

8 3. Write a program that will accept a number x from the user and evaluate y using the following function: y = x2 cos (2x + 1) (6x)log (x) 4. Write a program to create two matrices x and y of 1x3 and 3x2 sizes respectively. The output of the program should be: a) Matrix multiplication of x and y b) Scalar multiplication of x with 7 c) Scalar addition of y with 10 The prelab report should include the code along with the output. You can copy paste the code/output from the command window to a word document, print it and then paste it on your notebook. Graphs should also be pasted to the report if there are any. 8