Generalized Mattig’s relation in Brans–Dicke–Rastall gravity

The geodesic deviation equation (GDE) is being studied in Brans–Dicke–Rastall (BDR) gravity. We briefly discuss the BDR gravity and then construct GDE for FLRW metric. In this way, the obtained geodesic deviation equation will correspond to the BDR gravity. Eventually, we solve numerically the null vector GDE to obtain from Mattig relation, the deviation vector [Formula: see text] and observer area distance [Formula: see text] and compare the results with [Formula: see text]CDM model.