ENGR 1181 Midterm Exam 2: Study Guide and Practice Problems

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1 ENGR 1181 Midterm Exam 2: Study Guide and Practice Problems Disclaimer Problems seen in this study guide may resemble problems relating mainly to the pertinent homework assignments. Reading this study guide and solving the practice problems is not a sufficient level of studying for this exam. Students should also review the relevant reading material and PowerPoint slides as questions will be asked from those places as well. 50 Points Total Exam Specifications 15 points multiple choice (~15 questions, 1 2 pts. each) o Done on Carmen using a lockdown browser o No other internet access is allowed. Those accessing the internet otherwise will be sent to COAM. Please review OSU s policy on academic misconduct. o Graded automatically and entered into Carmen. 35 points 2 show your work problems o Both problems will focus on MATLAB, you may need to fill in the blanks with code, or create a script file, or modify a script file. Always start your script files by displaying your name, seat number etc. and using close all; clear; clc o Make sure you assign a different name for each PDF file during the exam. o Do not use run section during the exam, it will not save your script file and your work will be lost! ALWAYS use run. Calculators are not allowed. The exam is closed book closed notes. No communication with other students is allowed. Please review OSU s policy on academic misconduct. No use of cell phones.

2 Content Review Below is contained the content and learning objectives that will be tested on this exam. Not all learning objectives will be tested exactly as read, however students should use this material to keep track of what they need to be reviewing. 1. MATLAB a. Array Creation i. [a, b, c ; d, e, f] notation ii. [min : step : max] notation iii. linspace function iv. I/O Demonstrate proper usage of basic MATLAB features (e.g., the Command Window, script files, other default windows, arithmetic operations, assigning variables and names, built in functions, help command) Demonstrate proper notation for accessing elements from previously assigned one dimensional arrays (e.g., single elements, list of elements) and two dimensional arrays (e.g., those with rows and columns) b. Array Accessing i. Pure array accessing ii. Sub arrays iii. Using the colon operator Demonstrate proper notation for accessing elements from previously assigned one dimensional arrays (e.g., single elements, list of elements) and two dimensional arrays (e.g., those with rows and columns) Explain that a string is a one dimensional array and can be used the same way as numeric arrays c. Array Operations (. Operators) Explain meaning of element by element operations Identify situations where the standard operators in MATLAB (when used with arrays) are reserved for linear algebra, which is not always element byelement Apply dot operators for o The six cases where linear algebra is not element by element and therefore dot operators are needed to produce element by element calculations d. MATLAB algebra syntax (conversion from math expression) Explain meaning of element by element operations

3 Identify need to translate mathematical notation into proper MATLAB syntax e. Conditional Statements and logical operators Explain how conditional statements (e.g., if end, if else end, switch case) are used to make decisions Apply logical operations correctly in arrays Analyze data using logical operators. f. MATLAB looping Use more complex ways of setting the loop index Use loops to repeat a code with conditional statements 2. Labs continued a. Solar Meter Describe and build both a calibration and solar meter circuit Convert decimal values to binary values Compare a pictorial image of a circuit to a schematic wiring diagram b. Solar Cell Identify the advantages and disadvantages of solar cells. Calculate the efficiency of a solar cell. c. Beam Bending Employ the concepts of stress, strain, and Young's modulus for structural materials. Use the stress strain equation to calculate how applied forces deform structures. Calculate the moment of inertia of various beam geometries. Determine how beam geometry affects the stiffness and strength of beams. Identify unknown beam material through analysis and calculation of Young s Modulus. Evaluate behavior of various beams based on material and shape. d. Wind Turbine part A Describe the relationship between velocity (of the wind) and pressure based on Bernoulli s Equation for incompressible flow. Calculate the power available in the wind and compare it to the power generated by a wind turbine. Summarize the characteristics of the wind tunnel and turbine. Describe the relationship between velocity (of the wind) and pressure.

4 Determine the power available in the wind. Relate the power available in the wind to the wind speed. Compare the power generated by a wind turbine to the power in the wind. Here is a syntax guide for help in reviewing. PRINTING AND BRINGING THIS TO THE EXAM IS NOT ALLOWED. MatLab Syntax Review Sheet FOR MIDTERM 2 RELEVANT INFORMATION ONLY Current Directory your current working directory with a list of m files Workspace current list of MatLab variables and values Command History past commands that have been typed and executed Command Window where commands can be entered Editor Window where you write and run MatLab script files Don t forget that typing help into MATLAB will assist you with specific functions and is allowed during the exam show your work problems! MatLab Tips >> clc clear command window; does not clear memory >> cmd displays the result of a command in the command window >> cmd; does not display the result in the command window >> cmd1, cmd2 displays both results >> cmd1; cmd2 displays last result only clear clear x,y,z variable names math precedence... (ellipsis) up arrow down arrow clears ALL variables from memory clears only x, y, and z 1. must begin with a letter 2. are case sensitive 3. contain letters, numbers, and _ highest ( ) ; ^ ; * / ; + lowest extends a command to the next line scrolls backward through previous commands scrolls forward through commands help abcd help on the subject "abcd" ( doc abcd works too )

5 Numeric Display Formats format short format long format short e format bank nnn.1234 nnn (14 decimal places) n.1234e+001 nnn.12 Input / Output Commands disp( ' any text ' ) fprintf('text = %i,%f',k,x) x = input( ' any text ' ) displays ' any text ' in the command window formatted output prints "Text = integer and fixed point" asks the user to enter a value for x from the keyboard 1 D Array (row and column vectors) scalar, s is a single number (a 1 x 1 array) vector, v is a 1 row x n column array a list of numbers v_list = [ a b c ] or = [ a, b, c ] row vector v_row = [ a b c ] or = [ a, b, c ] column vector v_col = [ a ; b ; c ] constant spacing v_space = [ first : space : last ] single spacing v_1space = [ first : last ] vector with n terms, evenly spaced v_nterms = linspace( first, last, n ) transpose of a vector v_col = v_row ' value of the ith term v(i) Addition / Subtraction z = x y z = [,, Multiplication / Division z = x.* y and z = x. / y Exponents z = x.^ y z = [.^,.^,.] max(v) or min (v) length(v) mean(v) or sum(v) Returns largest / smallest element of v Returns the length (# of elements) in vector v Returns average value / sum of elements in v 2 D Array (matrix) Matrix, A is an r (rows) X c (columns) array A( r, c ) is the value of the element ( r, c ) in A A( r, c ), in rows A = [ row1 ; row2 ; row3 ] A( r1:r2, c1:c2 ) retrieves values in row and column ranges Example: A(1:3, [1 4 6]) means rows 1 3 and columns 1,4,6 of matrix A

6 Logic Conditional and Relational Operators Less than / Greater than < / > Less than equal to / greater than equal to <= / >= Equal to / Not equal to == / ~= TRUE statement / FALSE statement 1 (or any non zero number) / 0 & AND ( Example: A & B ) TRUE when A and B are both true OR ( Example: A B ) TRUE when either A is true or B is true ~ NOT ( Example: ~ A ) TRUE if A is false / FALSE if A is true Operator precedence ( high low ) ( ) ^ ~ */ + > < >= <= == ~= & Conditional Statements if ( conditional statement) Command Group end Works when there is only one command group if ( conditional statement) Command Group 1 else Command Group 2 end if ( conditional 1 ) Command Group 1 elseif ( conditional 2 ) Command Group 2 elseif ( conditional 3 ) Command Group 3 else Command Group 4 end If the conditional statement is "True", then do "Command Group 1". It the conditional statement is "False", then do "Command Group 2". "If elseif elseif else end" When there are more than two command groups, you can use this form with elseif Elseif = if not the first, do the second, or if not the second, do the third, etc. The "else" never has a conditional and is optional.

7 Loops k = first : step : last Loop index variable = first value : step size : last value Example of a loop in a script file: v1 = [ 0 : 5 : 25 ] ; % Define the vector v1 This loop calculates a new vector v2 from an existing vector v1. Note that the loop uses vector addressing. for i = 1 : length (v1) % The step size is 1 v2(i) = v1(i) ^ 2 ; % calculates a new element in the vector v2 end disp(v2) Common Functions sqrt(x) exp(x) abs(x) log(x) log10(x) factorial(x) sin(x) / cos(x) / tan(x) sind(x) / cosd(x) / tand(x) round(x) fix(x) ceil(x) floor(x) rem(x,y) if rem(x,y) == 0 sign(x) square root of x = exponential function absolute value of x natural log of x log base 10 of x factorial function [ x! ], where x is a positive integer trig functions with angle in radians trig functions with angle in degrees Round to the nearest integer Round toward zero Round toward infinity Round toward negative infinity Equals the remainder of x divided by y Conditional test that is true when x is a multiple of y Signum function returns [1 if x>0], [ 1 if x<0], [0 if x=0]

8 ENGR 1181 Midterm 2 Review Worksheet Note: This practice material does not contain actual test questions or represent the format of the midterm. The first 29 questions should be completed WITHOUT using MATLAB. 1) Answer the following questions according to the screen shot of MATLAB below: a. Label all 6 items (Command Window, Editor Window, etc ) b. What is the primary purpose of the Workspace? What is stored there? c. If a data file does not appear in #2, is it readily available to load into MATLAB?

9 2) Is Hello ENGR 1181 Student.m an acceptable file name for an.m file? If not, how could we modify it so that it is? 3) True or False, it is good practice to define all of the variables you need for a script file directly in the Command Window before you run your code. TRUE FALSE 4) What will MATLAB Output for entering the following in the Command Window? y=5(3)+2 5) What command clears the MATLAB workspace of all variables? 6) Given the variable pi= is defined in your workspace, how would you write one line of code to reference this variable and display: To the command window? The value of pi is ) Given the code below: k=0; for i = 1:3 end k k= 1+k+i;

10 What value of k will be displayed in the command window? 8) Given the list of variable names below, determine whether they would be good practice to use in MATLAB (or if they even work). If not, briefly explain why: a. The_greatest_variable_name b. J.T. Barret c. mean d. length e. 2manyloveENGR1181 f. time 9) Write 1 line of code that prompts the user to input their name as a string, and stores it to the variable name : 10) Write 1 line of code that creates an array v that starts at the value 2, goes to 100, and has 195 data points in between.

11 11) Write 1 line of code that creates an array u that starts at a value of 7 and goes to the value 27 with increments of 2. 12) What is the last value of the array X generated by the command below? X = (1:2:8) 13) Given the array A, answer the following questions: A= [ ] a. Write one line of code that extracts the first four elements of A: b. Write one line of code that extracts the 5, 6, and 9 th elements of A and assigns them to the variable B: c. Write one line of code that extracts the odd elements of A and assigns them to the variable Odd: 14) Given the matrix M below, answer the following questions: a. Write one line of code that extracts the last two rows, and all the columns of M:

12 b. Write one line of code that extracts all the rows, and the odd columns of M: c. Write one line of code that extracts rows 1 2 and 4, and all the even columns of M and stores it to the variable C: d. Write one line of code that extracts the even rows and columns 3 and 4 of M: 15) Given the code below, what will be the value of z when the for loop is complete? Y = linspace(1,10,1200); for z = 1:length(Y) q = 1 + 1; end z 16) Based on the code below, what will be displayed to the Command Window once the script has run? t = 3; d = 1; While t < 10 end t d t = t+2; d = d+1;

13 17) Compare and contrast for loops and while loops. When might it be better to use one over the other? 18) Write a command that starts a timer called tstart 19) What is 1 line of code that will check the time of the timer tstart 20) The modulus of elasticity is defined as: a) The ratio of yield stress to strain (y s /ε) in the plastic region. b) The slope of strain to stress (ε/σ) in the elastic region. c) The slope of stress to strain (σ/ε) in the elastic region. d) The ratio of stress to strain (σ/ε) in the plastic region. e) The slope of stress to material stiffness (σ/e) in the elastic region. 21) Write the command to create a vector, X, starting at 50 and ending at 5 with values every 0.2, which displays the created vector in the command window.

14 22) What is the command to use a built in system function to find the average of the vector X from question #1 above, assign the value to RESULT, and suppress output in the command window? 23) If C = [ ] and D = [7 8 9], what is the command to create a single row array X with the elements of C and D (afterwards X = [ ])? 24) Write the command to find the sine of 30? 25) The Solar Meter Lab used a Trim Pot (Trim Potentiometer) in the breadboard setup. When you turn the knob on the TrimPot, which variable is adjusted? 26) Given that x=[ ; ; ] has been assigned, what would be the result of y=x(2:3,[1 2 4])? 27) Write a single statement that prompts the user with 'Please enter the day of the week: ' Assign the results to a variable called 'today', suppressing any outputs to Command Window. 28) Given a 10 by 3 matrix M, write a single command that extracts all members of the 3 rd column of matrix M and assigns it to a vector called M_col_3 using the colon operator. 29) A vector x is defined in MATLAB by: x = [1:2:7]; Consider the equation: y Write a MATLAB command that creates a vector y where each element has a value calculated by the equation with the corresponding element in the vector x.

15 ENGR 1181 Exam 2 Show Your Work Review You are being assigned two problems. Complete each problem in a separate script file. Include comment statements to help organize your script file and try to implement flexible coding. Include the standard header. Problem 1 Background You are an engineer who loves to play pranks at the office. Your co worker has MATLAB up on the screen, and has exited their cubical to go to the restroom your time to strike. Problem Statement Given your Halloween spirit, you want to make it appear as if a ghost is typing on their screen. In this problem, prompt the user to enter the message they want to *magically* appear on their coworker s screen. After inputting the command, clear the Command Window. Utilizing a for loop and a new function called the pause()command, have the program type out the sentence in the command window one character at a time. Once the program is finished, display the total elapsed time the program took to run in the command window. HINT: In the command window, enter doc pause for more information on the pause command. IMPORTANT: You will NOT be responsible for knowing the pause() command for the upcoming midterm. It is simply being used as a tool to complete this problem. Problem 2 Background Environmental Engineers often take measurements of large data sets to analyze how conditions of a system are being impacted by a population or concentration value. This could apply to many difference facets, wildlife population, chemical contamination, etc Problem Statement PART 1 You are an environmental engineer who needs to analyze duck population data of Mirror Lake in order to put together an ecology report. Your main goal is to find out on average how many ducks were on the pond each year. You have obtained a file called duck_data.txt that records the year (column 1) and the rounded average number of ducks in the Mirror Lake for that year (column 2) from

16 In a script file, develop a program that can analyze the years from Extract two vectors and name them as duck and year. Keep in mind that these values were generated off of measurements in the field. PART 2 Your coworker left you with the formula that estimates the number of Crested Ducks per year (Y) as a function of the average number of ducks per that year (X): (NOTE: Afroduck is a Crested duck, google it!).3.2 Using array extraction and a for loop calculate the average of the number of Crested Ducks on Mirror lake from (1 value). Communicate this result to the command window using fprintf(). NOTE: means floor the values within the brackets