Try this:
numRows = size(db,1)-1;
rowsToDelete = false(numRows, 1);
for k = 2 : numRows % Has to start at 2, right? Since you're using k-1. Don't use i, the imaginary variable, as a loop index.
if db.INTERVENTION(k)==1 && isequal(db.SETTLEMENTDATE(k-1),db.SETTLEMENTDATE(k)) && isequal(db.DUID(k-1),db.DUID(k))
rowsToDelete(k) = true;
end
end
db(rowsToDelete, :) = []; % Remove these rows.
% Or equivalently
%db = db(~rowsToDelete, :); % Extract everything BUT the rows to delete.
