Practice Questions (with answers) for Second Midterm

The Final Exam (May 15 4-6pm in BA 259) will focus on these questions,
as well as the questions from the first midterm

This URL: http://www.stewart.cs.sdsu.edu/cs205/midterm2/midterm2_with_answershtml

NOTE: I hope you have examined the solution for midterm one Midterm 1 Solutions

I plan to pose these questions in the same manner as our first midterm. So you will be asked to give the contents of the MATLAB Workspace and some of the problems, that are still evolving, will involve user-defined functions.

Loops and Control Statements

Suppose we have a vector containing a group of distance values that represent the distance of a cable car from the nearest tower. We want to generate a coresponding vector containing velocityies. If the cable car is within 30 feet of the tower, we use the equation:
velocity = 0.425 + 0.00175 * d^2
If the cable cable is further than 30 feet from the tower, we use the follwing equation:
velocity = .625 + 0.12 * d - 0.00025 * d^2
Assume there are 25 elements in the given vector d, and write the appropriate MATLAB code to compute the corresponding velocities.
```
for k = 1:25
    if d(k) <= 30
       velocity(k) = 0.425 + 0.00175*d(k)^2;
    else
       velocity(k) = 0.625 + 0.12*d(k) - 0.0025*d(k)^2;
    end
end
```

Consider the following switch/case statement

% assume the input value is in centimeters and this MATLAB code
% converts to the units specified by the variable, units
x = 2.7;
units = 'm';
disp([' for input ' num2str(x) ' in centimeters, this fragment converts to '])
switch units % convert x to centimeters
	case {'inch','in'}
		y = x * 2.54 
	case {'feet','ft'}
		y = x * 2.54 * 12 
	case {'meter','m'}
		y = x/100 
	case {'millimeter','mm'}
		y = x*10 
	case {'centimeter','cm'}
		y = x 
	otherwise
		disp(['Unknown Units: ' units])
		y = nan;
end
disp( units )

Gives the output:

for input 2.7 in centimeters, this fragment converts to
y =
   0.0270
m

With the same source fragment above, what output will be computed for the case of

x = 1025;
units = 'ft';

The output would be:

for input 1025 in centimeters, this fragment converts to
y = 31242
ft

Strings

Give the output for the following MATLAB commands:

y = 45; s = num2str(y); title = [ ' Data for ' s ' cows in a pasture']
```
title =

   Data for 45 cows in a pasture
```
msg = 'You''re right!'
```
msg =

You're right!
```
msg(1:3)
```
ans = 

You
```
msg(8:12)
```
ans =

right
```

v = ['Character strings having more than'
     'one row must have the same number '
     'of columns just like arrays!      ']

v =

Character strings having more than
one row must have the same number
of columns just like arrays!

lawyers = char('Cockran', 'Shapiro', 'Clark', 'Darden')

lawyers =

Cockran
Shapiro
Clark
Darden
 size(lawyers)
ans =

    4     7

Timing

The routines tic, toc were introduced to allow the programmer to determine the amount of CPU needed to complete a sequence of commands.

In the switch code fragment above, indicate below were you could insert calls for timing

% assume the input value is in centimeters and this MATLAB code
% converts to the units specified by the variable, units
x = 2.7;
units = 'm';
disp([' for input ' num2str(x) ' in centimeters, this fragment converts to '])

tic

switch units % convert x to centimeters
	case {'inch','in'}
		y = x * 2.54 
	case {'feet','ft'}
		y = x * 2.54 * 12 
	case {'meter','m'}
		y = x/100 
	case {'millimeter','mm'}
		y = x*10 
	case {'centimeter','cm'}
		y = x 
	otherwise
		disp(['Unknown Units: ' units])
		y = nan;
end

toc 

disp( units )

Graphics

Vector Operations

Draw a rough diagram of the expect MATLAB output for the following sequence of commands:

x = linspace(0,10,100); % create data
y = sin(x);
z = (y>=0) .* y; 
z = z + 0.5 * (y<0);
z = (x <=8) .* z;
plot(x,z),...
xlabel('x'),ylabel('z = f(x)'), title('A Discontinuous Signal')

File I/O

Draw a rough diagram of the expected MATLAB output for the following sequence of commands (this will involve a separate file):

% set up data
x = 0:10; y = [x; x.^2];
fid = fopen('exp.txt','w') % open a file for writes
fprintf(fid,' %g %g \n ',y)

What are the contents of the file exp.txt?

Practice Questions (with answers) for Second Midterm

The Final Exam (May 15 4-6pm in BA 259) will focus on these questions,as well as the questions from the first midterm

The Final Exam (May 15 4-6pm in BA 259) will focus on these questions,
as well as the questions from the first midterm