library(pacman)
p_load(deSolve)

p = 0.03
yini = 1000

derivs = function(t, y, parms)
    list(y*p)

times = (seq(from=0, to=10, by=1))

out = ode(y=yini, times = times, func = derivs, parms = NULL)

head(out, n=10)