Interpretation of coal compositional data on whole-coal versus ash bases through the weighted symmetric pivot coordinates method - Xu, Na (China University of Mining and Technology (Beijing). College of Geoscience and Survey Engineering) ; Wang, Ru (China University of Mining and Technology (Beijing). College of Geoscience and Survey Engineering) ; Engle, Mark A. (University of Texas at El Paso. Department of Earth, Environmental and Resource Sciences) ; Zhu, Wei (China University of Mining and Technology (Beijing). College of Geoscience and Survey Engineering) ; Li, Qiang (China University of Mining and Technology (Beijing). College of Geoscience and Survey Engineering) ; Wang, Zhiwei (China University of Mining and Technology (Beijing). College of Geoscience and Survey Engineering)