how to figure it out

[sally]

i have a big problem.

my model is about a inventory model.

at the time (t), i have to do two things, one is to check do i have the receiving , if i have, i need to add the receiving quantity to the inventory. then to check do i have to place the replenishment order, the other thing is to do the customer demand,( to minus the customer demand.)



i am confused about the order in vensim, and how to set up it?

summary: i have to check do i have the receiving at time t, then to check do i have the replenishment order, then to check the custome's demand .



and

[bob@vensim.com]

A simple formulation is below - the molecules show better ones. See also books on System Dynamics such as Sterman's text.

Inventory = INTEG(receipts - shipment,initial inventory)

receipts = other formula

shipments = MIN((inventory + TIME STEP*receipts)/min order fill time,orders)

min order fill time = TIME STEP

[sally]

what dose time step means?


when do i need to use it in my model?

when i set up a model, i always fact the unit problems,

such as, if invetory is a level (case), customer demand is a Aux(case), and sales(case/day) is Min(inventory, customer demand), i will see the unit wrong message, How to figure it out?

attachment is my practice model.

[sally]

the attachment...

thank you .