http://arxiv.org/abs/1503.01444http://thoh.kaist.ac.kr/Research/PartialSum/PartialSum.htmAcknowledgment [NCRC];
The first author was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2010-0028680).
The first author was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2010-0028680).