How to get a subarray from a matrix

Hi. I am looking to solve this Question: Write a function called top_right that takes two inputs: a matrix N and a scalar non-negative integer n, in that order, where each dimension of N is greater than or equal to n. The function returns the n-by-n square array at the top right corner of N.

So I am looking to take the top right portion of matrix N to get a subarray that is n by n units. I thought the code might look like this:

function M = top_right(N,n)
M = N(end-n+1:end, 1:n);

However, this gives me the bottom left of the matrix and i want the top right.

[Star Strider]

Context: What is wrong with my code?

[yasin Sanjar]

try M= [N(1:n,end-n+1:end)]

[aklapaz]

Hi Sanjar, could you explain the logic behind this part of your script?: end-n+1:end

Thanks

[Karthik Subramanian]

Lets say you have 5 columns. Top right and n=2 means you need last two columns. So you should count till end and you start from the last before column which is end-n+1 = 5-2+1 = 4 . As you need columns 4 and 5.

[Vijay Ramanathan]

I was trying M= [N(1:n,end-n+1:end)] with M= [N(1:n,end-n:end)] before i saw your answer. I thought it wont apply for all but later it did :) Thanks Karthik and Yasin

[Stephen23]

In all of the above comments the square brackets are superfluous.

Answer 1

[James Tursa]

Switch your row and column indexing. E.g.

M = N(1:n,end-n+1:end);

Answer 2

[Star Strider]

That’s different than the wording of your earlier Question.

As far as the indexing code, see if this does what you want:

N = randi(99,8,6)                           % Argument Matrix
[R,C] = size(N);
min_dim = min(R,C);
n = randi(min_dim-1)                        % Argument Parameter
M = N(1:n, C-n+1:C)                         % Return Top Right Corner Square Matrix

N =

      79    65    20    86    17     8
      10    49     4    80    97    52
      26    78    74    58    71    10
      34    71    50    19    50    81
      68    90    48    24    47    81
      14    89    90    88     6    72
      72    34    61     3    68    15
      11    70    62    49     5    66

n =

       3

M =

      86    17     8
      80    97    52
      58    71    10

Answer 3

[Aakriti Mittal]

function N=top_right(M,n) T = M(1:n,1:n); N=T; Try this code...Hopefully it will work.. Aakriti

[Guillaume]

• please learn to format your answer
• You're answering a two year old question. Hopefylly, the OP is still not waiting for an answer
• Your function returns the top left portion of the matrix, not the top right
• What is the point of

T = ...; 
N = T;

? Why not write directly

N = ...;

and not have an intermediate variable that serves zero purpose?