can't put an if statement in a differential equation - r

Question

Hi guys i have been battling to get this ODE working but i keep coming across this error : Error in eval(expr, envir, enclos) : object 'j' not found
My code is below and it seems to be an issue with my if statement in the ODE
parameters <- c(
a = 0.032,
b = (9 / 140),
c = (5 / 1400),
d = (95 / 700),
k = 1 / 140,
i = 0.25,
# r = 0.2,
n = 6000000,
x = 0.3 ,
t = 1 / 180, # important in looking at the shape
u = 1 / 180, # important in looking at the shape
v = 1 / 360, # important in looking at the shape
p = 10,
s = 10000,
g = 100
# e = .4,
#h = 1000
)
state <- c(
S = 5989900,
E = 100,
I = 100,
Q = 100,
D = 100,
B = 100,
C = 100,
Y = 100,
H = 1000,
R = 1000,
J = 1000,
h = 100,
e = 0.1,
r = 0.1
)
# set up the equations
equation <- (function(t, state, parameters)
with(as.list(c(state, parameters)), {
# rate of change
dS <- (-(a * S * I) / n) - (((1 / r) * S * D) / n)
dE <- (a * S * I) / n + (((1 / r) * S * D) / n) - i * E
if (h > Q)
j = 1
else if (h < Q)
j = 0
dI <- i * (j) * E - (e) * I - c * I - d * I
dQ <- (j) * (e) * I - b * Q - k * Q
dD <- d * I - r * D
dB <- b * Q + r * D
dC <- c * I + k * Q
dY <- p * (b * Q + r * D)
dR <- (1 - x) * (p * (b * Q + r * D)) - t * (R)
de <- t * (s / R)
dJ <- (x) * (p * (b * Q + r * D)) - v * (J)
dr <- v * (s / J)
dH <- (x) * (p * (b * Q + r * D)) - u * (H)
dh <- u * (H / g)
# return the rate of change
list(c(dS, dE, dI, dQ, dD, dB, dC, dY, dR, de, dJ, dr, dH, dh))
}))
#
# solve the equations for certain starting parameters
library(deSolve)
times <- seq(0, 200, by = 1)
out <-
ode(y = state,
times = times,
func = equation,
parms = parameters
)
# , method = "vode"
head(out)
tail(out)
# graph the results
par(oma = c(0, 0, 3, 0))
plot(out, xlab = "Time", ylab = "People")
#plot(out[, "X"], out[, "Z"], pch = ".")
mtext(outer = TRUE, side = 3, "Ebola Model",cex = 1.5
)
any help would be great!

Answer 1

In case when h==Q variable j won't be created.
In given example h is equal Q.
You should add else statement or assign base value to j before if statements.
Like this:
j = 0
if (h > Q){
j = 1
}
else if (h < Q) {
j = 0
}
or
if (h > Q){
j = 1
}else if (h < Q) {
j = 0
}else{
j = 0
}