How can i stop loop if all matrix elements are similar?

The matrix is modified in each iteration. When all elements of matrix are similar i want to stop the iteration. For example i tried by using codes shown below but it doesnt work. May you help me for solving this problem?

iteration=0;
np=10;
W=zeros(np,1);
while iteration<1000
Wupdate %The sub-script that modify the matrix
if np*W(1)==sum(W)
iteration=10000
end
end

Answer 1

[Matt J]

if max(W(:))-min(W(:))<=tolerance
  break;
end