minor bugfix
minor bugfix

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