Equivalent of an Octave command in MATLAB

Question

I'm trying to realise the following Octave command in MATLAB:

M = eye(x)(y,:);

x is just a number (in my example 10) and y is a vector (here 8x1):

y = [1 3 4 5 7 10 9 10];

The Octave command would generate:

M =

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

The ones are kept very near to the diagonal.

The nearest I came with MATLAB is with the following commands:

n = size(y,1);
Y = eye(n, x);

but it would generate something still different. If the difference between rows and columns gets bigger, it would be very different.

M =

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

How could I get the first matrix with MATLAB?

The 6th row of your first M array is awkward... do you confirm? — Ratbert, Jul 29 '17 at 20:40
You can't chain indices like that in MATLAB, you have to put `eye(x)` in a temp variable. — beaker, Jul 29 '17 at 20:47
What beaker meant: `M = eye(x);` ‍‍‍‍‍‍ ‍‍‍‍‍‍ `M= M(y,:);` — Sardar Usama, Jul 29 '17 at 20:48
I would suggest you to read your error message: `()-indexing must appear last in an index expression.` — m7913d, Jul 29 '17 at 20:51
The duplicate target I linked shows you some of the approaches if you're interested. However the simplest (and the best) way is to use a temporary variable. — Sardar Usama, Jul 29 '17 at 20:53

score 0 · Answer 1 · answered Jul 29 '17 at 20:50

0

First you should find what this expression eye(x)(y,:) means. First create an identity matrix with the size of x by x, and then select rows with index in y. Therefore, the equivalent syntax would be:

 E = eye(x);
 M = E(y,:);

answered Jul 29 '17 at 20:50

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Equivalent of an Octave command in MATLAB

1 Answers1