If/else statements

If a parameter value depends on a condition, it can be written with in Mlxtran with the usual if-else-end syntax. For example, if a parameter c should be 1 if t<=10, 2 if t<20 and 3 otherwise, write

CODE

if t<=10
   c = 1
elseif t<20
   c = 2
else
   c = 3 
end

Conditional derivatives

Derivatives cannot be written within an if-else-end structure. Instead, intermediate variables should be used. For example, if a derivative of x over time should be 1 if t<=10 and 2 otherwise, write

CODE

if t<=10
   dx = 1
else
   dx = 2
end
ddt_x = dx

Example: count model

Some models from the Count model library are defined with if/else statements, such as the zero-inflated Poisson model:

CODE

[LONGITUDINAL]
input= {lambda0, nu, f}

EQUATION:
lambda = lambda0*exp(-t/nu)

DEFINITION:
CountNumber= {type=count, 
    if k==0
        Pk = exp(-lambda)*(1-f) + f
    else
        Pk = exp(k*log(lambda) -lambda -factln(k))*(1-f)
    end
P(CountNumber=k) = Pk}

OUTPUT:
output= CountNumber