# Make sure that your first graph is still open,
# and that the original graph was drawn so that
# the y-axis goes from 0 to 3.5
y_vals = c(0, 3.5)
# Vector of initial conditions
y_0 = seq(0.2, 2, by = 0.2)
# For-loop
for (i in 1:length(y0)) {
# Re-set start each time
start = c(x_0, y_0[i])
# Solve the ODE
output = as.data.frame(rk4(start, times, odef, parms))
# Plot our values on the same graph
par(new = TRUE)
plot(output$"2",
type = "l",
col = c(i),
ylab = "",
xlab = "",
ylim = y_vals,
xaxt = "n",
yaxt = "n")
}