From: Sensor models and localization algorithms for sensor networks based on received signal strength
NLS
VNLS(x) = (y - h(x))TR-1(x)(y - h(x))
GML
VGML(x) = (y - h(x))TR-1(x)(y - h(x))+log detR(x)
ML
VML(x) = log pe(y - h(x))