.estimateLength -- Attempts to anticipate how many return values a pattern will yield before stopping. It's impossible to predict exactly in every case, but for simple patterns the number might be close enough.

Pseries.fromEndpoints(start, end, length)

Pgeom.fromEndpoints(start, end, length)

Given the desired starting and ending values, and number of output values, the correct step size or ratio will be calculated for you. The length must be finite and greater than 1.