CODEWITHSUNDEEP
matlab
user2048267
user2048267

Reputation:

Create Matrix using Matrix Indices

In matlab, how could you create a matrix M using its indices to populate the values? For example, say I want to create a 3x3 matrix M such that

M(i,j) = i+j --> [ 2 3 4; 3 4 5; 4 5 6]

I tried making vectors: x = 1:3', y = 1:3 and then

M = x(:) + y(:)

but it didn't work as expected.

Any thoughts on how this can be done?

Thanks!

UPDATE

The M I actually desire is: 

M(i,j) = -2^(-i - j).

Upvotes: 3

Views: 272

Answers (3)

Mohsen Nosratinia
Mohsen Nosratinia

Reputation: 9864

You should use bsxfun to find the sum: 

M=bsxfun(@plus, (1:3).', 1:3)

and for the second formula:

M=-2.^(-bsxfun(@plus, (1:3).', 1:3))

Upvotes: 2

Daniel
Daniel

Reputation: 36710

bsxfun(@(x,y)(-2.^(-x-y)), (1:3).', 1:3)

This uses the Answer of Mohsen Nosratinia with the function you wished.

Upvotes: 1

jkshah
jkshah

Reputation: 11703

One way would be

x = 1:3;
z = ones(1,3);
N  = z'*x + x'*z
M  = -2 .^ -(z'*x + x'*z)
% Or simply 
% M = -2 .^ -N

Output:

N =

   2   3   4
   3   4   5
   4   5   6

M =

  -0.250000  -0.125000  -0.062500
  -0.125000  -0.062500  -0.031250
  -0.062500  -0.031250  -0.015625

Upvotes: 1

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