How to create a matrix using Booleans that looks like this:

I'm trying to teach myself Matlab. I want to create a 5x5 matrix that looks like this: A= [1,1,1,1,1;6,1,1,1,1;7,7,1,1,1;8,8,8,1,1;9,9,9,9,1]

I've tested this so far:

a=@(i,j) (abs(i-j)<=1)+(i+j)+(abs(i-j)>1)*j;;A=create_matrix(a,5,5)

^^This is the closest I've gotten but it's not even close. Any hints appreciated. Thanks

I made the following script...

function [A] = create_matrix(a,n,m)
A = zeros(n,m);
for i=1:n
for j=1:m
A(i,j)=a(i,j);
end
end
end

Answer 1

[Voss]

A = ones(5); % initialize A as a 5-by-5 matrix of all ones
for ii = 1:size(A,1)
    A(ii,1:ii-1) = 4+ii; % fill in each row up to but not including the diagonal with the appropriate value
end
A

A = 5×5

1 1 1 1 1 6 1 1 1 1 7 7 1 1 1 8 8 8 1 1 9 9 9 9 1

Of course the first row remains all ones, so the loop could be for ii = 2:size(A,1)

You might also be able to use tril or other functions to do the same.

[Voss]

Or did this need to use Booleans (known as logicals in MATLAB lingo) specifically, for some reason?

If so:

A = ones(5);
[m,n] = size(A);
[jj,ii] = meshgrid(1:m,1:n);
A(ii > jj) = ii(ii > jj)+4;
A

A = 5×5

1 1 1 1 1 6 1 1 1 1 7 7 1 1 1 8 8 8 1 1 9 9 9 9 1

Answer 2

[John D'Errico]

There are always a million ways to solve such a problem, however, there is no need to use booleans at all. Best is if you learn to visualize what various tools can give you.

My immediate solution is the simple:

n = 5;
m = 5;
triu(ones(n,m)) + tril((n:2*n-1)' + zeros(1,m),-1)

ans = 5×5

1 1 1 1 1 6 1 1 1 1 7 7 1 1 1 8 8 8 1 1 9 9 9 9 1

Note that it should be fairly easy to follow what I did, and that is always important.

Even slightly simpler is this related one:

ones(n,m) + tril((n-1:2*n-2)' + zeros(1,m),-1)

ans = 5×5

1 1 1 1 1 6 1 1 1 1 7 7 1 1 1 8 8 8 1 1 9 9 9 9 1

But then you should see why this will work, and is simpler yet.

1 + tril((n-1:2*n-2)' + zeros(1,m),-1)

ans = 5×5

1 1 1 1 1 6 1 1 1 1 7 7 1 1 1 8 8 8 1 1 9 9 9 9 1

I'll quit now, before I add 5 more solutions.