modify_case_rx_new.m

function mpc = modify_case_rx_new(mpc, ulim, N, verbose)
	rng(0);
	if nargin == 1
		ulim = 0.9;		% default upper limit on branch R/X ratio is 0.9
		verbose = 0;
	elseif nargin == 2
		N = 0;          % if 0, cap the high R/X ratio to be ulim; otherwise, change N random lines R/X ratios 
		verbose = 0;
	end
	
	branch = mpc.branch;
	
	found_large_rx = false;
	if N == 0
		for i = 1:size(branch(:,1))
			rx_i = branch(i, 3) / branch(i, 4);
			if rx_i > ulim
				found_large_rx = true; 
% 				prompt = strcat('Branch (', num2str(branch(i,1)), ', ', num2str(branch(i,2)), ...
% 						') has R/X ratio: ', num2str(rx_i), ', greater than the specified upper limit: ', ...
% 						num2str(ulim), '. Type 1 to change to the upper limit, and 2 to ignore.');
% 				answer = input(prompt); 
				answer = 1;
				if answer ~= 1
					continue;
				elseif answer == 1
					branch(i, 3) = ulim * branch(i, 4);  
					rx_i_new = branch(i, 3) / branch(i, 4);
					if verbose
						fprintf('>>> R/X ratio of branch (%4d, %4d) changed from %5.4f to %5.4f.\n', branch(i,1), branch(i,2), rx_i, rx_i_new);
					end
				end
			end
		end
		if ~found_large_rx && verbose
			fprintf('No branch R/X ratio exceeding %.3f exists in this system.\n', ulim);
		end
	else 
		E = size(mpc.branch, 1);
		idx = randi(E, N, 1);    % change N random branches to have high RX ratio = ulim
		for i = 1:N
			rx_i = branch(idx(i), 3) / branch(idx(i), 4);
			mpc.branch(idx(i), 3) = mpc.branch(idx(i), 4) * ulim;
			fprintf('R/X ratio of branch (%4d, %4d) changed from %5.4f to %5.4f.\n', branch(idx(i),1), branch(idx(i),2), rx_i, ulim);
		end
	end
	
	mpc.branch = branch; 
	
	%% sanity check
	for i = 1:size(branch(:,1))
		rx_i = branch(i, 3) / branch(i, 4);
		if rx_i > ulim
			warning('Bug: branch R/X ratio exceeding %.2f still exists\n', ulim)
		end
	end
end