Takes the inverse difference (e.g. goes from diff() result back to previous vector)
intgr_vec(x, xi, lag)diff_inv_values(x, lag, d, xi)
diff_inv(x, lag, d)
A vec containing the data
A vec with length \(lag*d\) that provides initial values for the integration.
An unsigned int indicating the lag between observations.
An unsigned int which gives the number of "differences" to invert.