In the chandas (Vedas) the affix vati (vat) is added to an upasarga (Preposition) in the sense of a verbal root.,
As the word उद्वतः and निवतः in the following Rik (X. 142. 4).
यदु॒॒द्वतो॑ नि॒॒वतो॒॒ यासि॒॒ वप्स॒॒त् पृथ॑गेषि प्रग॒॒र्धिनी॑व॒॒ सेना॑ ॥ \When thou O Fire ! goest burning high (उद्वतः = उद्गतान्) and low (निवतः = निगतान्) trees &c.,