how to create a matrix from a part of another matrix?

x= [1 54 61 23;71 4 79 33;12 34 65 89;]

I need to have y=[1 54;71 4] i meen, "y" must take the values X (1,1) (1,2) (2,1) (2,2)

how can i do it????

Answer 1

[Star Strider]

You essentially already did it. You simply need to use the correct index references:

x= [1 54 61 23;71 4 79 33;12 34 65 89]; 
y =  x(1:2, 1:2);

[Rachuan]

thanks and sorry, i didnt expresses what i nedded.

Ngl=2

x= [1 54 61 23;71 4 79 33;12 34 65 89;]

I need y=size(Ngl,Ngl) and to take the first values of the x Matrix inside "y"

[Star Strider]

This code:

x = [1 54 61 23;71 4 79 33;12 34 65 89]; 
Ngl = 2;
y = x(1:Ngl, 1:Ngl)

produces:

y =

       1    54
      71     4

[Rachuan]

It does, however if Ngl=1 y=[1;71] while the correct answer would be y=[1]

Ngl=3 y=[1 54 61;71 4 79] correct y=[1 54 61;71 4 79;12 34 65]

[Star Strider]

That is not the result I get:

Ngl = 1
y = x(1:Ngl, 1:Ngl)

produces:

Ngl =

       1

y =

       1

and this code:

Ngl = 3
y = x(1:Ngl, 1:Ngl)

produces:

Ngl =

       3

y =

       1    54    61
      71     4    79
      12    34    65

If you want to add a limit to be certain ‘Ngl’ does not exceed the size of ‘x’, the code becomes:

Ngl = 3
Ngl = min([Ngl size(x)]);
y = x(1:Ngl, 1:Ngl)

With this check, ‘y’ will always be square, will start at the first row and column indices of ‘x’, and ‘y’ will not attempt to get values of ‘x’ that are beyond the index limits of ‘x’.