The function is written from the scratch. The result has been
compared against the 'Matlab' `filter`

function with one-dimensional
real inputs. Other situations such as matrix `b`

or multi-dimensional
`x`

are not implemented.

## Arguments

- b
one-dimensional real numerical vector, the moving-average coefficients of an

`ARMA`

filter- a
the auto-regressive (recursive) coefficients of an

`ARMA`

filter- x
numerical vector input (real value)

- z
initial condition, must have length of

`n-1`

, where`n`

is the maximum of lengths of`a`

and`b`

; default is all zeros