Engineering Questions with Answers - Multiple Choice Questions
Strassen’s Algorithm MCQ’s
1 - Question
Strassen’s algorithm is a/an_____________ algorithm.
a) Non- recursive
b) Recursive
c) Approximation
d) Accurate
View Answer
Answer: b
Explanation: Strassen’s Algorithm for matrix multiplication is a recursive algorithm since the present output depends on previous outputs and inputs.
2 - Question
What is the running time of Strassen’s algorithm for matrix multiplication?
a) O(n2.81)
b) O(n3)
c) O(n1.8)
d) O(n2)
View Answer
Answer: a
Explanation: Strassen’s matrix algorithm requires only 7 recursive multiplications of n/2 x n/2 matrix and Theta(n2) scalar additions and subtractions yielding the running time as O(n2.81)
3 - Question
What is the running time of naïve matrix multiplication algorithm?
a) O(n2.81)
b) O(n4)
c) O(n)
d) O(n3)
View Answer
Answer: d
Explanation: The traditional matrix multiplication algorithm takes O(n3) time. The number of recursive multiplications involved in this algorithm is 8
4 - Question
Strassen’s matrix multiplication algorithm follows ___________ technique.
a) Greedy technique
b) Dynamic Programming
c) Divide and Conquer
d) Backtracking
View Answer
Answer: c
Explanation: Strassen’s matrix multiplication algorithm follows divide and conquer technique. In this algorithm the input matrices are divided into n/2 x n/2 sub matrices and then the recurrence relation is applied
5 - Question
The number of scalar additions and subtractions used in Strassen’s matrix multiplication algorithm is ________
a) O(n2.81)
b) Theta(n2)
c) Theta(n)
d) O(n3)
View Answer
Answer: b
Explanation: Using Theta(n2) scalar additions and subtractions, 14 matrices are computed each of which is n/2 x n/2. Then seven matrix products are computed recursively.
6 - Question
Running time of Strassen’s algorithm is better than the naïve Theta(n3) method.
a) True
b) False
View Answer
Answer: a
Explanation: Strassen’s Algorithm requires only 7 recursive multiplications when compared with the naïve Theta(n3) method which reuires 9 recursive multiplications to compute the product.
7 - Question
Given the program of naïve method.
for i=1 to n do for j=1 to n do Z[i][j]=0; for k=1 to n do ___________________________
Fill in the blanks with appropriate formula
a) Z[i][j] = Z[i][j] + X[i][k]*Y[k][j]
b) Z[i][j] = Z[i][j] + X[i][k] + Y[k][j]
c) Z[i][j] = Z[i][j] * X[i][k]*Y[k][j]
d) Z[i][j] = Z[i][j] * X[i][k] + Y[k][j]
View Answer
Answer: a
Explanation: In the naïve method of matrix multiplication the number of iterating statements involved are 3, because of the presence of rows and columns. The element in each row of one matrix is multiplied with each element in the column of the second matrix. The computed value is placed in the new matrix Z[i][j].
8 - Question
Who demonstrated the difference in numerical stability?
a) Strassen
b) Bailey
c) Lederman
d) Higham
View Answer
Answer: d
Explanation: The difference in the numerical stability was demonstrated by Higham. He overemphasized that Strassen’s algorithm is numericaly unstable for some applications.
9 - Question
What is the recurrence relation used in Strassen’s algorithm?
a) 7T(n/2) + Theta(n2)
b) 8T(n/2) + Theta(n2)
c) 7T(n/2) + O(n2)
d) 8T(n/2) + O(n2)
View Answer
Answer: a
Explanation: The recurrence relation used in Strassen’s algorithm is 7T(n/2) + Theta(n2) since there are only 7 recursive multiplications and Theta(n2) scalar additions and subtractions involved for computing the product.
10 - Question
Who discussed techniques for reducing the memory requirements for Strassen’s algorithm?
a) Strassen
b) Lederman
c) Bailey
d) Higham
View Answer
Answer: c
Explanation: The submatrices formed at the levels of recursion consume space. Hence in order to overcome that Bailey discussed techniques for reducing the memory required.
11 - Question
What is the formula to calculate the element present in second row, first column of the product matrix?
a) M1+M7
b) M1+M3
c) M2+M4 – M5 + M7
d) M2+M4
View Answer
Answer: d
Explanation: The element at second row, first column can be found by the formula M2 + M4, where M2 and M4 can be calculated by
M2= (A(2,1) + A(2,2)) B(1,1)
M4=A(2,2)(B(1,2) – B(1,1)).
12 - Question
Strassen’s Matrix Algorithm was proposed by _____________
a) Volker Strassen
b) Andrew Strassen
c) Victor Jan
d) Virginia Williams
View Answer
Answer: a
Explanation: Strassen’s matrix multiplication algorithm was first published by Volker Strassen in the year 1969 and proved that the n3 general matrix multiplication algorithm wasn’t optimal
13 - Question
How many iterating statements are involved in the naïve method of matrix multiplication?
a) 1
b) 2
c) 3
d) 4
View Answer
Answer: c
Explanation: In the naïve method of matrix multiplication the number of iterating statements involved are 3, because of the presence of rows and columns in a matrix. The element in each row of the first matrix is multiplied with each element in the column of the second matrix.
14 - Question
Strassen’s algorithm is quite numerically stable as the naïve method.
a) True
b) False
View Answer
Answer: b
Explanation: Strassen’s algorithm is too numerically unstable for some applications. The computed result C=AB satisfies the inequality with a unit roundoff error which corresponds to strong stability inequality(obtained by replacing matrix norms with absolute values of the matrix elements).
15 - Question
Compute the product matrix using Strassen’s matrix multiplication algorithm.
Given a11=1; a12=3;a21=5;a22=7
b11=8;b12=4;b21=6;b22=2
a) c11=20;c12=12;c21=100;c22=15
b) c11=22;c12=8;c21=90;c22=32
c) c11=15;c12=7;c21=80;c22=34
d) c11=26;c12=10;c21=82;c22=34
View Answer
Answer: d
Explanation: The solution can be obtained by
C11=1*8 + 3*6 =8+18=26
C12=1*4 + 3*2 =4+6=10
C21=5*8 + 7*6 =40+42=82
C22= 5*4 + 7*2=20+14=34.