how to remove some row or column of a matrix at once?

lets say i have a 100x100 matrix and i want to remove row 71-100 so it become 100x70 matrix

Answer 1

[Arthur]

a = zeros(100,100); %create 100x100 matrix
a(71:100,:) = []; %remove rows 71:100

Answer 2

[Sean de Wolski]

Note you say row but the new size of your matrix removed columns

Here are two ways to remove columns:

x = x(:,1:70); %glass half full

or

x(:,71:end) = []; %glass half empty