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Conditional Statements

How to create a conditional statement​

Python if statements won't work when applied to TemporalVar instances. To implement conditional Temporal Variables, use vip.where(condition, a, b).

The expression variable = vip.where(condition, a, b) means that the value of variable is a at times when the condition is True, and b otherwise.

Why if doesn't work​

TemporalVar instances can't behave correctly with regular if statements. Using if will evaluate the entire TemporalVar object as a boolean, which ignores its temporal nature. Because it is ambiguous, a ValueError is raised when an if is applied to a TemporalVar.

To illustrate the issue, let's say we want to create the following step function:

f(t)={0if t<51if t≥5f(t) = \begin{cases} 0 & \text{if } t < 5 \\ 1 & \text{if } t \geq 5 \end{cases}

❌ Don't do this​

danger

This code does not work:

time = vip.temporal(lambda t: t)
if time < 5:
    step = vip.temporal(0)
else:
    step = vip.temporal(1)

vip.solve(10, time_step=1)

✅ Do this instead​

tip

Use vip.where() to define the conditional behavior in a single expression:

time = vip.temporal(lambda t: t)
step = vip.where(time < 5, 0, 1)

step.to_plot()

vip.solve(10, time_step=0.01)

Step plot