added abstract and minor changes
added abstract and minor changes

SheffieldML/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/GPmat