cost: initial cost of asset
salvage: value after depreciation
life: number of periods
start_period: first period to accumulate for
end_period: last period to accumulate for
factor: factor at which the balance declines
no_switch: do not switch to straight-line depreciation
VDB calculates the depreciation of an asset for a given period range using the variable-rate declining balance method.
If no_switch is FALSE, the calculation switches to straight-line depreciation when depreciation is greater than the declining balance calculation.