How to fill in a zeroes matrix using data from a separate array.

I am trying to work out how to fill in a matrix of zeroes to represent precedence requirements.

I have a 40x40 matrix of zeroes, and each collumn and row represent the tasks 1:40. I also have a 121x2 matrix with the precedent requirements. This is such that if a task needs to be completed before a different task can start, the first task is listed in collumn one and the second in collumn two.

I want to represent this in the form of having a matrix of 1s and 0s where a 1 is placed in row 1 collumn 2, it shows that task 2 relys on task one having happened. If there is a 0 there is no precedence requirement.

Is there a way i can take my 121x2 matrix and populate the 40x40 matrix accordingly? I assume it will be through a loop of reading each like of the 121x2 matrix and populating the 40x40 in this way but i wouldn't know how to approach the code for this.

Thank you in advance for any support.

[Dyuman Joshi]

"Is there a way i can take my 121x2 matrix and populate the 40x40 matrix accordingly? "

Yes, you can use indexing to do that.

How you can utilize indexing will depend on the assignment is to be done.

Answer 1

[Matt J]

Sounds like a job for accumarray, e.g,

requirements=[1 2; 2 3; 3 4; 4 6; 5 8]

requirements = 5×2

1 2 2 3 3 4 4 6 5 8

matrix = accumarray(requirements,1,[40,40])

matrix = 40×40

0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

[Bella Alcock]

Thank you so much, this has worked!

[Matt J]

I'm glad, but please Accept-click the answer to indicate that.

Answer 2

[Voss]

Here's one way to do that, demonstrated with smaller matrices:

% a 3x2 matrix of precedence requirements, in lieu of your 121x2 matrix, for simplicity.
% task 1 must be completed before task 2; 2 before 3; 3 before 4:
precedence = [1 2; 2 3; 3 4]

precedence = 3x2

1 2 2 3 3 4

% 4x4 matrix of zeros, in lieu of your 40x40 matrix, for simplicity
M = zeros(4,4)

M = 4x4

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

% put the 1s in place. this will work for your matrices too
idx = sub2ind(size(M),precedence(:,1),precedence(:,2));
M(idx) = 1

M = 4x4

0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0

Reference: https://www.mathworks.com/help/matlab/ref/sub2ind.html

[Bella Alcock]

Thank you so much!

[Voss]

You're welcome!