BIL 113E
Int. to Sci. & Eng. Comp. (MATLAB)
March 16, 2018
Answer the questions in the spaces provided. If you run out of room for an answer,
continue on the back of the page.
Name Surname:
Student Number:
1. (a) The function given below can be used to encrypt a string. How would you call it in Matlab?
function [ encryptStr ] = encrypt( originalStr, offset )
%encrypt - this function performs a simple encryption of a given string.
%Each character is converted by the given offset in the ASCII table.
(b) You wish to write a script that will analyze the following function:
y=
2x2 cos(x)
exp 0.1x
Write the m-file, fun_x.m, required to define this as a MATLAB function.
2. We have made a function triangleArea(xvec,yvec) that can be used to find the area of a triangle.
The help for the function is shown below.
>> help triangleArea
triangleArea (xvec, yvec) returns the area of a triangle.
Argument is xvec, a vector containing the three x-coordinates of the triangle,
and yvec, the three y-coordinates of the triangle.
You have a triangle with the coordinates given by the figure below. Write a call to the function with
correct parameters.
3. If matrix A is defined in MATLAB as A = [1,4,3,2 ; -3,4,-5,1 ; 5,6,1,2 ; -2,-3,5,6] What is
the output of the commands?
(a) A(1:3 , 2:3)
BIL 113E
Int. to Sci. & Eng. Comp. (MATLAB), Page 2 of 4
March 16, 2018
(b) A(1,:)
(c) A(:,3)
(d) C = A(2:3,:)
4. A student produced the following script, eqnsolver.m, in response to a programming assignment to
create a script that would solve a set of linear equations given an augmented coefficient matrix file.
1. % script to solve linear set of equations
2. % A*x = b
3. % requires augmented coefficient matrix file
4.
5. header( )
6.
7. % get augmented coefficient matrix, decompose
8. % to coefficient matrix, Amat, and right hand side, rhs
9. disp(’ ’)
10. fname = input(’Augmented coefficient matrix file name? ==> ’);
11. augmat = load(fname);
12. [Nrow, Ncol] = size(fname);
13. Amat = augmat(:,1:Nrow);
14. rhs = augmat(:,Ncol);
15.
16. % solve system
17. soln = Amat/rhs;
18.
19. % display results
20. disp(’ ’)
21. disp(The solution vector is)
22. disp(soln)
However, the following messages appeared when the student attempted to run the script using a properly
configured augmented coefficient matrix , called test.dat, as a test case. Your job is to (1) find the
offending line of code and (2) show a fix to the error in the spaces provided below the message.
(a) ??? Error: File: C:\temp\eqnsolver.m Line: 5 Column: 13
Expected a variable, function, or constant, found ")".
(b) Augmented coefficient matrix file name? ==> test.dat
??? Undefined variable ’test’ or class ’test.dat’.
BIL 113E
Int. to Sci. & Eng. Comp. (MATLAB), Page 3 of 4
March 16, 2018
(c) ??? Index exceeds matrix dimensions.
Error in ==> C:\temp\eqnsolver.m
On line 14 ==> rhs = augmat(:,Ncol);
(d) ??? Error using ==> /
Matrix dimensions must agree.
Error in ==> C:\temp\eqnsolver.m
On line 17 ==> soln = Amat/rhs;
(e) ??? Error: File: C:\temp\eqnsolver.m Line: 21 Column: 14
")" expected, "identifier" found.
(f) What will be displayed if help eqnsolver is entered at the command window prompt?
Hint: A sample augmented matrix is defined as below
a b e
A=
c d f
which represents the following sets of equation.
ax + by = e
cx + dy = f
5. Given the following matrix, show the results generated by the MATLAB command.
R = [1.22 3.78 2.41]
fprintf(’R = %3.1f \n’, R)
6. Write the MATLAB commands to generate a table of conversions from knots to m/s. The range of
knots should be from 0 to 30 in increments of 5. Note 1 knot = 0.5144 m/s.
7. Write a MATLAB program to prompt the user for a time constant tc and a max time tmax, then
generate a plot of v = exp(−t/tc). Hint: The time interval is between 0 and tmax.
BIL 113E
Int. to Sci. & Eng. Comp. (MATLAB), Page 4 of 4
March 16, 2018
8. Consider the following MATLAB script. What are the values for a, b and c after it is run?
a=3.2;
b=10;
c=2;
if (c>(a+b))
a=b-c;
else
a=b^2;
end
b=a+(c^2);
a
b
c
9. Use one if-statement to rewrite the following nested if-statement
if w < x
if w > y
w = x*y
end if
end if
10. Given vectors x=[-1, 2, 3, -2], y=[0.2, 3.1, 0, -3] and z=[3, 0, 1, 0.1], provide answers to
the following operations.
(a) x < y > z
(b) x + ~ y > z
(c) x == y ~ =z
Hint: ~ means logical not. An element of the output array is set to 1 if A contains a zero value element
at that same array location. Otherwise, that element is set to 0.