4x4 matrix with numbers from 1 to 4 in specific order

Hi,

I want to create the following matrix:

M = 1 2 3 4

0 0 0 3

0 0 0 2

0 0 0 1

I'm only supposed to use the vector r = 1:4 and no other functions. This is what I got so far:

M=r

M(1:4, 4)=r

But this results in

M = 1 2 3 1

0 0 0 2

0 0 0 3

0 0 0 4

So now I'm stuck. Does anybody know how to "reverse" the last column so that it reads 4 3 2 1 instead of 1 2 3 4?

All help is greatly appeciated!

Cheers,

Dobs

Answer 1

[Image Analyst]

You need to put r in in reverse order, so assuming you're not allowed to use flipud(r), try:

r = 1:4
M(1:4, 4)= r(end : -1 : 1);

Then you need to set row 1:

M(1, ......................

[Dobs]

Yes, that worked! Thank you so much!

Answer 2

[John D'Errico]

Hint: What does flip do? Could you use it to "flip" the order of those numbers?

[Dobs]

I think we're not allowed to use it since we're only supposed to use the vector r and no other functions. But I just tried it and it works too! Will keep this in mind for the next time I need to reverse the numbers in a vector. Thank you so much for your help!