TY  - JOUR
AU  - Tohidi, G.
AU  - Tohidnia, S.
TI  - Productivity changes of units: A directional measure of cost Malmquist index
JO  - Journal of New Researches in Mathematics
VL  - 1
IS  - 2
SP  - 55
EP  - 66
PY  - 2015
DO  - 
ER  -