Physics 210 UBC/Fall 2014

Quiz 2 - Go!!

Instructions

All of the commands that you use to complete this quiz must be entered in the file
```
/phys210/$LOGNAME/matlab/q2.m
```
The first statement in this file must be
```
q2_setup
```
If this line is not included you will be unable to complete the quiz. Also, if you prefer to work the questions interactively and then transfer your answers to q2.m be sure to type
```
>> q2_setup
```
before you do anything else.
q2_setup is a script that defines 13 variables: 8 row vectors
```
v1, v1_el, m1_row, m1_col, w1, w2, w3 and w4
```
and 5 matrices
```
m1, a1, a2, a3, a4
```
You can display any of these by simply entering their names at the Matlab prompt, but be warned that v1 and m1 contain many elements. I'll leave it as an exercise for you to determine how many.
Try to answer the questions using as few Matlab statements as possible, but note that in several cases it may be advantageous to first copy a vector or matrix and then modify it, i.e,
```
>> foo1 = foo
>> foo1(...) = ...
```
I will use (copy) to label the instances where I suggest you do this.

I will indicate the number of statements you are expected to use in the parenthesis following the question label, that number will include assignment statements used to copy arrays.
IMPORTANT: Several questions ask you to create vectors or matrices by selecting subsets of elements other vectors and matrices. Unless specified otherwise, the elements in the new arrays should be in the "same order" as those in the original.

Example 1: Given
```
a = 1  2  3  4  5  6  7  8  9  10
```
the vector
```
a1 = 3  9  10
```
is a subset of elements of a that are in the "same order" whereas
```
a2 = 9  3  10
```
is not.

Example 2: Given
```
m =
    10  15  20  25  
    30  35  40  45
    50  55  60  75
```
the matrix
```
m1 =
    10  25
    50  75
```
is a subset of elements of a that are in the "same order" whereas
```
m2 =
    20  15
    35  40
```
is not.

I will denote the questions where the order of elements is to be preserved in this manner with (order)

OK, on with the quiz, and remember that the first line in q2.m, or the first command that you type should you wish to first solve the problems interactively, must be

q2_setup

Q2.1 (1)

Assign to v1_length the number of elements of v1.

Q2.2 (1)

Assign to m1_m and m1_n the number of rows and columns, respectively, of m1 (try to do it with a single assignment statement).

Q2.3 (order, 1)

Define v2 to be a column vector that contains the following elements of v1:

10056  24493  26631  27740  36992  45365  56733  62284  65056  84730

(e.g 10056 means the 10056-th element of v1)

Q2.4 (order, 1)

Define m2 to be the matrix that contains all elements of m1 that are in one of the following rows:

53    59    73   106

and one of the following columns:

158   255   340

Q2.5 (order, 1)

Define v3 to be the column vector containing elements 53400 through 53451, inclusive, of v1.

Q2.6 (order, copy, 2)

Define v4 to have all of the elements of v3 except the 15th and 27th. Do not use a : operator, use element deletion.

Q2.7 (order, 1)

Define m3 to be the matrix that contains all elements of m1 that are in one of rows 35 through 39, inclusive, and one of columns 102 through 107 inclusive.

Q2.8 (order, copy, 3)

Define m4 to be the matrix containing the elements of m3 with the following modifiations: (1) All elements of the middle row of m3 except the last one have been replaced by 0. (2) All elements of the last column of m3 have been replaced by 1's.

Q2.9 (order, 1)

Define m5 to be the matrix that contains all elements of m1 that are in one of rows 25, 38, 51, ... 220, 233 and one of columns 10, 52, 94, .., 346, 388.

Q2.10 (order, copy, 2)

Define m6a to be the matrix resulting from the deletion of every third row of m5 starting with the second (i.e. delete rows 2, 5, 8). Use row deletion.

Q2.11 (copy, 2)

Define m6b to be the matrix in which the entries in column 8 of m5 have been reversed.

Q2.12 (1)

Define a row vector v5 which contains the following elements:

The elements of w1, followed by the elements of w2 in reverse order, followed by every 8th element of w3 starting with the 6th, followed by the 8th from last and last element of w4.

Q2.13 (copy, 3)

Define a column vector v5a which contains the elements of v5, with the first 10 elements replaced by 0 and the last 10 by the integers from 11 through 20 in reverse order.

Finishing up

IMPORTANT

When you've completed the quiz, execute the following from the terminal command line:

% date > /phys210/$LOGNAME/matlab/date

YOU CAN THEN WORK ON THE HOMEWORK OR TALK TO ME ABOUT YOUR TERM PROJECTS WHILE YOU WAIT FOR THE CLASS TO FINISH THE QUIZ