In stata, the fixed effect model(xtreg y x1 x2 x3, fe) report a constant term. The underline estimate is [y{it} - \bar{yr} + \bar{\bar{y}} = a + (x{it} - \bar{x{i}} + \bar{\bar{x}})) \alpha + (\epsilon{it} - \bar{e_i} + \bar{v})] with the constrant (\bar{v}) equals to 0. Details can be found on Stata’s website.
In R, plm package does not calculate the some whate artificial1 intercept for within models.
see help(“within_intercept”, package = “plm”)↩