How do I create a variable H which contains the product of 5 and the values of B in the 1st and 9th rows, and the 1st and 2nd column.

3 views (last 30 days)
Given: B=rand(randi([10 20]),randi([5 30]))
Find: Create a variable H which contains the product of 5 and the values of B in the 1st and 9th rows, and the 1st and 2nd column. Variable H must be of size [2 2].
Issue: I am unfamiliar with the wording, does it want 5 * the values of B in ([1,9],[1,2])?
My Solution: I got as far as to state >> H=prod(B([1,9],[1,2])); but I do not know what to do with "the product of 5" piece.
  3 Comments

Sign in to comment.

Accepted Answer

John D'Errico
John D'Errico on 20 Feb 2024
Edited: John D'Errico on 20 Feb 2024
Ok, first, you do understand how to extract the elements from B. Good there. I think maybe the question wording is confusing you.
B=rand(randi([10 20]),randi([5 30]))
B = 15×6
0.5745 0.6058 0.5994 0.6935 0.0956 0.2848 0.8822 0.8884 0.9519 0.3293 0.0266 0.6770 0.4545 0.1755 0.2823 0.9036 0.6515 0.7482 0.7823 0.5347 0.4965 0.6685 0.5269 0.4783 0.8030 0.9700 0.4688 0.5584 0.8849 0.9196 0.7843 0.5541 0.7347 0.1885 0.2401 0.6638 0.4241 0.2129 0.2587 0.7451 0.0305 0.8609 0.9187 0.1319 0.1306 0.4830 0.0690 0.1599 0.5090 0.7634 0.5069 0.6934 0.1676 0.5085 0.2144 0.5469 0.5273 0.1173 0.4948 0.9835
B([1,9],[1,2])
ans = 2×2
0.5745 0.6058 0.5090 0.7634
So the result is a 2x2 array.
The question is not asking you to form the product of all those elements. So there is no reason to use the function prod.
The clue is the result itself must be a 2x2 array. So now all you need to do is multiply all elements of that 2x2 array by the number 5. So you are correct that
5*B([1,9],[1,2])
ans = 2×2
2.8726 3.0291 2.5449 3.8168
is what appears to have been requested.
  3 Comments

Sign in to comment.

More Answers (1)

VBBV
VBBV on 20 Feb 2024
Do you mean like this ?
B=rand(randi([10 20]),randi([5 30]));
H = 5*kron(B([1,9]),B([1,2]).')
H = 2×2
2.0647 1.3872 2.0548 1.3806
  1 Comment
Kyle Weaver
Kyle Weaver on 20 Feb 2024
Edited: Kyle Weaver on 20 Feb 2024
I don't think we have learned about kron, (Kronecker tensor product), however I do appreciate your efforts and it did return H with size [2 2].

Sign in to comment.

Categories

Find more on Creating and Concatenating Matrices in Help Center and File Exchange

Products


Release

R2023b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!