# Why is this equation different in 2 different sources?

• I
Gold Member
In article "A note on the gravitoelectromagnetic analogy" by Matteo Luca Ruggiero (https://arxiv.org/pdf/2111.09008v1.pdf) equation number 18 is ##\nabla \dot\ E=4 \pi G \rho##
, but corresponding equation in the wikipediapage(https://en.wikipedia.org/wiki/Gravitoelectromagnetism#Equations) is ##\nabla \dot\ E_g=-4 \pi G \rho_g##
. ##E## notes same thing in the article as ##E_g## on the wikipedia page. ##\rho## note same thing in the article as ##\rho_g## on the Wikipedia page. Why is this equation different in these sources? To me seems that Wikipedia equation is correct, because from it follows that direction of gravitational field is directed to (not away from) bodies(with positive mass).

vanhees71