Function db

db(
    cost: number,
    salvage: number,
    life: number,
    period: number,
    month?: number,
): number
Calculates the depreciation of an asset for a specified period using the fixed-declining balance method.

Remarks:
- The fixed-declining balance method computes depreciation at a fixed rate. Uses the following formulas to calculate depreciation for a period: `(cost
  - total depreciation from prior periods) * rate, where rate = 1 - ((salvage / cost) ^ (1 / life))`, rounded to three decimal places.
- Depreciation for the first and last periods is a special case. For the first period, this function uses this formula: cost * rate * month / 12
- For the last period, DB uses this formula: ((cost - total depreciation from prior periods) * rate * (12 - month)) / 12
Parameters
- cost: number
  The initial cost of the asset.
- salvage: number
  The value at the end of the depreciation (sometimes called the salvage value of the asset).
- life: number
  The number of periods over which the asset is depreciated (sometimes called the useful life of the asset).
- period: number
  The period for which you want to calculate the depreciation. Period must use the same units as life.
- Optionalmonth: number = 12
  The number of months in the first year. If month is omitted, it is assumed to be 12.
Returns number
the depreciation
Example
```
db(1000000, 100000, 6, 1, 7); // 186083.33333333
```
- Defined in db.js:29