num
If c(t) is the current capacity and b(t) is the current number busy, then a(t) = c(t) - b(t) is the current number of available units. Under some capacity change situations, a(t) may be negative.
If c(t) is the current capacity and b(t) is the current number busy, then a(t) = c(t) - b(t) is the current number of available units. Under some capacity change situations, a(t) may be negative.