R.QGAMMA 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.QGAMMA inverts a gamma probability to obtain a nonnegative cutoff for valid positive shape and scale. Its default probability is lower-tail; FALSE switches to an upper-tail probability. The function uses scale, not rate. Versioned function help.

=R.QGAMMA(probability,shape,scale[,lower_tail[,log_p]])

• probability: 0–1 normally, or its natural logarithm with log_p=TRUE.
• shape: required and positive.
• scale: required and positive for a valid gamma distribution; validate it explicitly.
• lower_tail, log_p: optional TRUE and FALSE respectively. The output is a cutoff in scale units, not a logged cutoff.

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; invalid-model observations are identified separately below. Results are rounded to twelve decimal places, or thirteen significant digits for small nonzero values. This is presentation precision, not a universal accuracy guarantee.

With shape=2 and scale=1, the median is approximately 1.678346990017 and the lower-tail 90th percentile is 3.889720169867. The 90th percentile is also the upper-tail 10th percentile.

Doubling scale to 2 doubles the median to approximately 3.356693980033. With shape=1 and scale=2, the median is 2×LN(2), approximately 1.386294361120.

=R.QGAMMA(LN(0.1),2,1,FALSE(),TRUE()) requests the upper-tail 10% cutoff using a logged input. It agrees with the ordinary upper-tail call. The saved inverse check sends the lower-tail 90th percentile to R.PGAMMA with the same parameters.

Quantiles scale linearly because the distribution is expressed in x/scale. That valid-model identity also explains the source defect: the implementation obtains a unit-scale cutoff and multiplies by scale without a positive-scale guard.

The saved advanced-check result for =R.PGAMMA(R.QGAMMA(.9,2,1),2,1) was 0.9.

The tested negative-scale result was approximately −1.678346990017 for probability 0.5 and shape 2; scale=0 returned 0. These are observed invalid-model results. Reject nonpositive scale before calculation instead of trusting the presence of a number. Shape=0 and negative shape were rejected.

For a valid positive scale, lower-tail probability 0 gives cutoff 0; probability 1 has an infinite cutoff and displays #NUM!. Upper-tail endpoints reverse those roles. In log mode, input 0 means probability 1. Positive log-probabilities and ordinary probabilities outside [0,1] are invalid.

F5 is genuinely empty, rather than a cell containing an empty string. #NUM! can represent an unrepresentable infinite mathematical endpoint as well as an invalid numeric domain; the distinctions above matter.

• Current worksheet callback
• Tested-version worksheet callback
• Current qgamma calculation
• Tested-version qgamma 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 identities were checked; secondary ODF exports retain these functions with the ORG.GNUMERIC namespace. GUI entry, other locales and other spreadsheet products were not tested.

GAMMAINV, GAMMADIST, R.QEXP.