EXPONDIST Function (Gnumeric)
EXPONDIST evaluates an exponential waiting-time model.
Verification status: See the evidence and test scope described in this guide. How formula examples are checked
Availability and version history
- Introduced: Documented by 1.12.62; original introduction not established.
- Availability: Supported in Gnumeric 1.12.62, based on the function-specific registration.
- Scope: Desktop; the fn-stat function module must be included and enabled.
- Checked: October 14, 2026. Official source and independent mathematical examples checked; Gnumeric 1.12.62 was not run.
What EXPONDIST does
EXPONDIST evaluates an exponential waiting-time model. Its second argument is the rate λ, so a mean waiting time of 2 minutes corresponds to rate 0.5 per minute. The final argument chooses a cumulative probability or a density. Official function reference.
For x≥0, CDF=1−exp(−λx) and density=λexp(−λx). Mean waiting time is 1/λ. Density has inverse-time units and is not the probability of an event at one exact time.
Syntax and arguments
=EXPONDIST(x,y,cumulative)
| Argument | Meaning |
|---|---|
| x | Nonnegative elapsed amount, often time. |
| y | Strictly positive rate λ, in inverse units of x. |
| cumulative | TRUE() for probability at or below x; FALSE() for density. |
Every argument shown is required. Use numeric inputs or cell references. The examples follow English Gnumeric’s comma-separated notation and decimal points; localized separators can differ. Release-pinned argument help and evaluator.
Reproducible examples
Enter each formula in an unused worksheet cell. These are independently calculated mathematical reference values rounded to twelve decimal places. Keep full stored precision in later formulas rather than retyping a rounded display.
| Formula | Expected result, approximately |
|---|---|
=EXPONDIST(0,0.5,TRUE()) |
0 |
=EXPONDIST(0,0.5,FALSE()) |
0.5 |
=EXPONDIST(1,0.5,TRUE()) |
0.393469340287 |
=EXPONDIST(1,0.5,FALSE()) |
0.303265329856 |
=EXPONDIST(3,0.5,TRUE()) |
0.776869839852 |
=EXPONDIST(3,0.5,FALSE()) |
0.111565080074 |
=EXPONDIST(2,1,TRUE()) |
0.864664716763 |
=EXPONDIST(2,1,FALSE()) |
0.135335283237 |
Worked worksheet applications
Probability by a deadline
Put elapsed time 3 in A2 and rate 0.5 in B2. Enter =EXPONDIST(A2,B2,TRUE()) in C2, expected 0.776869839852. The model assigns about 77.69% probability to a wait of three minutes or less. It assumes the constant-rate exponential model is suitable; the function does not fit that model from observations.
Surviving beyond a time
The mathematical survival probability is =EXP(-B2*A2), expected 0.223130160148 for the same inputs. It avoids forming 1 minus a CDF very near 1. To find the 90th-percentile wait at rate 0.5, use =-LN(1-0.9)/0.5, approximately 4.605170185988 minutes.
Release-specific errors and cautions
Rate versus scale: the help argument label calls y a scale parameter, but the displayed formula and release evaluator use it as a rate. The implementation passes 1/y as the scale to its exponential helper. Enter the reciprocal of a mean waiting time, not the mean itself. Negative x or y≤0 returns #NUM! in the wrapper. Pinned evaluator.
Advanced check and numerical interpretation
For this distribution, P(T>s+t | T>s)=exp(−λt). With λ=0.5 and an additional two-minute wait, the expected conditional survival probability is 0.367879441171, regardless of how long the model has already waited. This memoryless property belongs to the model and should not be assumed for aging equipment without justification.