How to select/pick specific 3*3 matrix from 6*6 matrix in MATLAB?

How to pickup any specific 3*3 or 2*2 or 4*4 matrix form any particular location from a global 6*6 or much bigger matrix. actually I am trying to find stiffness of stiffness of 2D frame using FEM in MATLAB. so to combine the matrix of every element in the global matrix. I need to pickup vaues for each node and combine common node.

can somebody help me here.

[Stephan]

you marked a 4x3 matrix instead 3x3

[Gaurav Sharma]

Ya my bad

Answer 1

[Stephan]

Hi,

for the lower right 3x3 matrix use:

A = k(4:end,4:end)

for the marked area (4×3):

A = k(3:end,4:end)

An upper left 2×2 would be:

A = k(1:2,1:2)

Best regards

Stephan

[Gaurav Sharma]

Thanks Stephen for your help. Cheers Mate