Coursera Machine Learning second week quiz answer Octave/Matlab Tutorial
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Octave Tutorial
5 Questions
1. Suppose I first execute the following Octave commands:
A = [1 2; 3 4; 5 6];
B = [1 2 3; 4 5 6];
Which of the following are then valid Octave commands? Check all that apply and assume all options are written in an Octave command. (Hint: A ‘sign the transpose of A.)
0.29926222492940724
C = A * B;
0.6644976132083684
C = B ‘+ A;
0.04820065735839307
C = A ‘* B;
0.18387076747603714
C = B + A;
Answer: ab (C = A * B and C = B ’+ A;)
2. Question text
Let A = ???? 16594211714310615138121 ????.
Which of the following indexing expressions gives B = ???? 16594211714 ????? Check all that apply.
0.06797481491230428
B = A (:, 1: 2);
0.46775804040953517
B = A (1: 4, 1: 2);
0.7515415323432535
B = A (0: 2, 0: 4)
0.40075311926193535
B = A (1: 2, 1: 4);
Answer: ab (B = A (:, 1: 2); and B = A (1: 4, 1: 2);)
3.Let A be a 10x10 matrix and x be a 10-element vector. Your friend wants to compute the product Ax and writes the following code:
v = zeros (10, 1);
for i = 1:10
for j = 1:10
v (i) = v (i) + A (i, j) * x (j);
end
end
How would you vectorize this code to run without any FOR loops? Check all that apply.
0.647465850925073
v = A * x;
0.9062917539849877
v = Ax;
0.990483850473538
v = x ‘* A;
0.4759985599666834
v = sum (A * x);
Answer: a. V = A * x;
v = Ax: Undefined function or variable ‘Ax’.
4. Say you have two column vectors v and w, each with 7 elements (i.e., they have dimensions 7x1). Consider the following code:
z = 0;
for i = 1: 7
z = z + v (i) * w (i)
end
Which of the following vectorizations correctly compute z? Check all that apply.
0.47586352098733187
z = sum (v. * w);
0.9338313168846071
z = w ‘* v;
0.03846661816351116
z = v * w ‘;
0.3784104809165001
z = w * v ‘;
Answer: ab (z = sum (v. * W); and z = w ‘* v;)
column vectors column vectors
5. In Octave, many functions work on single numbers, vectors, and matrices. For example, the sin function when applied to a matrix will return a new matrix with the sin of each element. But you have to be careful, as certain functions have different behavior. Suppose you have a 7x7 matrix X. You want to compute the log of every element, the square of every element, add 1 to every element, and divide every element by 4. You will store the results in four matrices, A, B, C, D. One way to do so is the following code:
for i = 1: 7
for j = 1: 7
A (i, j) = log (X (i, j));
B (i, j) = X (i, j) ^ 2;
C (i, j) = X (i, j) + 1;
D (i, j) = X (i, j) / 4;
end
end
Which of the following correctly compute A, B, C, or D? Check all that apply.
0.23870734148658812
C = X + 1;
0.7951180564705282
D = X / 4;
0.24619056400842965
B = X. ^ 2;
0.8001980590634048
B = X ^ 2;
Answer: abc
B = X. ^ 2 instead of X ^ 2
Coursera machine learning Week 2 Quiz answer Octave / Matlab Tutorial
