A 
submatrix of an 
matrix (with 
, 
) is a 
matrix formed by taking
a block of the entries of this size from the original matrix.
Submatrix
See also
MatrixExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Submatrix." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Submatrix.html