Function stdev

Population standard deviation. Valid scalar defaults accumulate squared deviations oldest first and omit nonfinite results. Supplied skip uses period finite observations and holds across gaps; propagate requires a full chronological window. Ties retain multiplicity; warmup is NaN. Invalid option-path periods throw RangeError, malformed options TypeError. A period must be a positive safe integer.

Bar-aligned lengths select the current population; NaN lengths give gaps. Arrays default to propagation.