R.PPOIS Function (Gnumeric)

• Introduced: First release not established; present in the retained 1.12.57 source.
• Supported in: Gnumeric 1.12.62; no retirement is established.
• Scope: Desktop Gnumeric with its Statistical Functions From R plugin. English comma-separated formulas are shown.
• Checked: October 14, 2026. Tables and the named advanced check use 1.12.57 ssconvert. Current 1.12.62 source was inspected; that release was not executed.

R.PPOIS returns the cumulative Poisson probability P(X≤cutoff). FALSE selects P(X>cutoff). The mean must describe the expected count over the same interval as the event count. Versioned function help.

=R.PPOIS(cutoff,mean[,lower_tail[,log_p]])

• cutoff: real threshold, with ordinary fractional values floored to the included integer count.
• mean: nonnegative expected count.
• lower_tail: optional TRUE for the lower cumulative probability; FALSE requests the upper tail.
• log_p: optional FALSE. TRUE uses natural-log probabilities, not base-10 logarithms.

Brackets mark optional arguments; do not type them. Current worksheet implementation.

These self-contained formulas were recalculated natively. Ordinary-domain results were checked against independent mathematics; source guards explain the boundary cases. Results are rounded to twelve decimal places, or thirteen significant digits for small nonzero values. This is presentation precision, not a universal accuracy guarantee.

At mean 2, cutoff 2 gives 0.676676416183. Cutoff 2.9 gives the same result because only counts 0, 1 and 2 are included. The strict upper tail at 2 is 0.323323583817, describing three or more events.

For two or more events, evaluate the upper tail at 1 instead. Independent arithmetic gives approximately 0.593994150290. The difference between “more than two” and “at least two” is the mass at exactly two, approximately 0.270670566473.

For nonnegative cutoff k, the lower probability is the finite sum EXP(-λ) times 1+λ+λ²/2!+…+λ^k/k!. This independently reproduces the examples without using the application’s gamma helper.

Lower and strict upper tails sum to one. Direct log mode at cutoff 2 and mean 2 returns approximately −0.390562087566 for the lower tail and −1.129101649751 for the upper tail. Prefer the direct tail you need, particularly when subtracting a result near one would lose useful digits.

The saved advanced-check result for =R.PPOIS(2,2)+R.PPOIS(2,2,FALSE()) was 1.

For mean zero, every nonnegative cutoff has lower probability one and upper probability zero. A negative cutoff still gives lower probability zero, including when the mean is zero. Negative means are invalid and give #NUM!.

The cumulative function floors an ordinary fractional cutoff; the mass function R.DPOIS instead returns zero for a genuinely noninteger event count. Empty F5 acts as zero, nonnumeric text gives #VALUE!, and a missing mean or surplus argument gives #N/A. Logarithms of zero become #NUM!. A probability calculation does not establish that a real process follows a Poisson model.

F5 is genuinely empty, rather than a cell containing an empty string.

• Current worksheet callback
• Tested-version worksheet callback
• Current ppois calculation
• Tested-version ppois calculation
• Nonfinite worksheet-value handling
• Statistical Functions From R plugin declaration

The relevant complete worksheet callback and main calculation helper are unchanged between the inspected versions. That does not establish later-version numerical execution. Both stale and uncached SUM controls recalculated correctly. Native XML preserves the R.* identities. The secondary ODF export keeps these calls in the ORG.GNUMERIC namespace; it does not establish execution in another product. GUI entry, other locales and other spreadsheet products were not tested.

POISSON, R.PGAMMA, R.DGAMMA.