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ECS 132, Spring 2023, Quiz 0

This is Quiz 0. It will be different from the other quizzes, which will be in-class (weekly in the disucssion section, and also in lecture on the last day of class).

Make SURE to read the instructions carefully.

Instructions

  • You must use the OMSI tool to submit your quiz. Make SURE to do a test run first, playing the role of both the student and instructor, as explained in the OMSI docs.

  • This will be due 11:59 pm, April 14. The TAs will start the OMSI server on April 3 (machine and port to be announced). You may submit at any time between April 3 and 14. Don't leave it for the last minute; keep in mind my slogan, "Computers never work." :-)

  • You should be able to get an A+ grade on this quiz! You are welcome to seek help from me or our TAs (you may ask more than once if needed):

    Norm Matloff, [email protected]
    Dylan Alberto Chima-Sanchez, [email protected]
    Lan Jiang, [email protected]

    You are not allowed to discuss this quiz with anyone else besides the three names listed above. Failure to adhere to this requirement will be considered a violation of the code of academic conduct.

  • Prepare for this quiz by learning the rudiments of R, in my fasteR tutorial, and by reviewing linear algebra, using my linear algebra review. Both topics will also be covered in discussion section, Week 1, but of course in less depth.

  • Quiz questions, both here and in future quizzes, will be labeled either "R code answer" or "Text answer." In the former case:

    • The OMSI grading tool will execute exactly what you submit. Accordingly, there should be NO non-R in your submission.

    • If the question asks for you to just write a function, that is all you must have in your submission. If you would like to include test code, do so and run to check but comment it out before submitting.

    • Use R comment lines to show your work and explain your answer.

    • A question may ask you to "print" something. This means, "print to the screen," i.e. use the print() function or equivalent.

    • When a question asks you to write code, it means it. Don't compute something by hand and then merely submit the number.

    • You are not required to include error-checking unless specifically asked to do so.

Regarding RStudio and the Tidyverse

Some of you may have been exposed to RStudio, an IDE for R. It's designed for noncoders, and in my opinion, VS Code is probably more appropriate for CS people. Personally, I find that IDEs in general just get in my way, and I just use the Vim text editor with my own homegrown macros. It's up to you. In any event, in terms of OMSI, it doesn't matter how you generate your R code; OMSI doesn't know and doesn't care.

A related issue is that some of you may have had some exposure to RStudio's Tidyverse, a set of libraries that essentially make radical changes to the basic R language ("base-R"). I've been rather critical of the Tidyyverse, and while I certainly don't mind your using it, there is a major practical question: Will the people grading your quizzes and homework (the TAs and myself) even have the Tidyverse on their machines? If they don't, your code won't run when they grade it. And even if the grader does have the Tidyverse installed, it may not be the latest version, again causing issues.

The quiz questions

Question 1: Consider the mtcars dataset, built-in to R. Write code that finds and prints the hp value in the third row of the dataset.

Question 2: Again with the mtcars dataset, write code that finds and prints the mean mpg among cars having 6 or 8 cyclinders.

Question 3: Again with the mtcars dataset, write code that adds a new column, the horsepower/weight ratio, and prints the entire new dataset, now 12 columns rather than 11.

Question 4: I live 60 miles from campus, and 1.5 miles from my nearest freeway exit. As I exited the freeway, the dashboard said I had averaged 34.2 miles per gallon on that trip (campus to freeway exit). When I got home, the figure was 33.8 miles per gallon for the entire trip (campus to my driveway). How many miles per gallon did I get from the freeway exit to home? Print this figure.

Question 5: Write code that finds the product of A and B below, using the %*% operator.

A <- rbind(1:2,5:6)
B <- rbind(1:3,5:7)
  # compute and print product here

Question 6: Write a function that creates and returns an n x n matrix whose row i, column j element is |i-j|.

ijMatrix <- function(n) 
{
   
  # add code here

}

Question 7: Write a function that creates and returns the value of a quadratic form, ut M u, for a vector u and matrix M. The result is a number.

quadForm <- function(u,M) 
{

  # add code here

}

Question 8: (Text answer.) What is the name of the matrix operation that exchanges rows with columns?