{ "category": "Compatibility", "display_name": "EXPONDIST", "entry_kind": "built_in_function", "eval_api": { "method": "POST", "url": "https://handbook.dnacalc.com/api/eval" }, "function_id": "FUNC.EXPONDIST", "implementation_state": { "answer_bank": { "excel_builds": [ "20430" ], "larger_numeric": 0, "last_bit": 0, "matched": 9740, "other_mismatch": 0, "refused": 0, "rows": 9740, "unread": 0, "worst_ulp": 0 }, "detail": "Recorded: 9,740 in the answer bank and 5 workbook cells.", "dnacalc_commit": "9e1884369a678158dd82d3d74188daf986995e87", "in_catalogue": true, "state": "matches", "state_label": "Matches every recorded Excel answer", "summary": "Matches all 9,745 recorded answers", "workbook_corpus": { "cells": 5, "matched": 5 } }, "implementations": [ { "commit": "9e1884369a678158dd82d3d74188daf986995e87", "flavour": "excel-compatibility-candidate", "language": "Rust", "name": "CalcFunc", "own_code": [ "https://github.com/DnaCalc/DnaCalc/blob/9e1884369a678158dd82d3d74188daf986995e87/crates/calc-func/src/catalogue/distributions.rs#L256-L259" ], "repository": "https://github.com/DnaCalc/DnaCalc", "shared_code": [ "catalogue/distributions::nums", "ported/discrete_dist::finite", "ported/discrete_dist::expon_dist_kernel", "ported/excel_numeric::binary_with", "ported/excel_numeric::excel_expm1_spilled", "ported/excel_numeric::expm1_internal_graph", "ported/excel_numeric::excel_x87_sub", "ported/excel_numeric::excel_x87_mul", "ported/excel_numeric::excel_x87_div", "ported/excel_numeric/x87::mul", "ported/excel_numeric/x87::sub", "ported/excel_numeric/x87::div", "ported/excel_numeric/x87_chains::pow2_positive", "ported/excel_numeric/x87_chains::pow2", "ported/excel_numeric/x87_chains::exp_ext", "ported/excel_numeric/x87_chains::exp_with", "ported/excel_numeric/x87_chains::excel_exp", "ported/excel_numeric/x87_chains::log_with", "ported/excel_numeric/x87_chains::excel_log" ], "source": "https://github.com/DnaCalc/DnaCalc/blob/9e1884369a678158dd82d3d74188daf986995e87/crates/calc-func/src/catalogue/distributions.rs#L256-L259", "state": "matches", "suite": null, "summary": "Matches all 9,745 recorded answers" } ], "json_url": "https://handbook.dnacalc.com/api/functions/FUNC.EXPONDIST.json", "name": "EXPONDIST", "notes": [], "schema": "efh.function-reference/v1", "section_order": [ "what-it-does", "try-it", "quirks", "how-to-implement", "version-differences", "alternatives" ], "sections": { "alternatives": "\n[GAMMA.DIST](FUNC.GAMMA.DIST.md) with shape one is related, but its scale transformation has its own stores. [WEIBULL.DIST](FUNC.WEIBULL.DIST.md) generalises the waiting-time shape.\n\n\n", "how-to-implement": "\nThe current kernel uses `R` for the [stored arithmetic operation](../model/09-staged-arithmetic.md), with the measured public LN and EXP leaves.\n\n1. Validate `x>=0` and `lambda>0`. Store `t=R(lambda*x)`. A nonfinite `t` gives `#NUM!`; replace a subnormal `t` with zero.\n2. For density, obtain `u=EXP(-t)` and return `R(lambda*u)` under the finite-result policy.\n3. For the CDF, obtain the same `u`. If it is exactly one, return `t`.\n4. Otherwise store `d=R(u-1)`. If `t<1`, store `c=R(R(d*(-t))/LN(u))`; otherwise use `c=d`. Return `-c`. Keep the product and division stores separate.\n5. The current finite-result helper turns nonfinite answers into `#NUM!` and flushes final subnormal answers to zero.\n\nFor the main example, `t=1`, `u` is about `0.36787944117144233`, and the CDF is about `0.632120558828558`. The density multiplies `u` by `0.5`. At `t=1e-20`, the public exponential rounds to one; returning `t` preserves the small CDF that direct subtraction would lose.\n\nThis is the stored Kahan correction also used by the [PMT discount recipe](FUNC.PMT.md#how-to-implement). The leaves and operation order are part of the candidate; substituting a language’s `exp` or `expm1` can change final bits. The problem report retains a numerical residual, so this is not a whole-domain equality claim.\n\n\n", "quirks": "\nNegative `x` or a nonpositive rate gives `#NUM!`; nonnumeric numeric arguments give `#VALUE!`. Zero time is admitted: the CDF is zero and the density is the rate. Do not pass a mean waiting time as `lambda` without taking its reciprocal.\n\nA naive `1-exp(-lambda*x)` can erase a small positive CDF when the exponential rounds to one. The current route has an explicit correction for this case. It also checks the stored rate-times-time product for overflow and flushes a subnormal product to zero, so a representable small CDF is not enough by itself to predict the published result.\n\n\n", "sources": "\n- [Microsoft: EXPONDIST function](https://support.microsoft.com/en-us/excel/functions/expondist-function), opened 6 November 2026; syntax, documented argument rules and errors.\n- [DnaCalc implementation](https://github.com/DnaCalc/DnaCalc/blob/da3ecc4fb19a3a5529708c311d0e8f05688ac165/crates/calc-func/src/ported/discrete_dist.rs); implementation steps and the limits identified in the text.\n- [Stored cancellation correction](https://github.com/DnaCalc/DnaCalc/blob/da3ecc4fb19a3a5529708c311d0e8f05688ac165/crates/calc-func/src/ported/excel_numeric/mod.rs), `excel_expm1_spilled`; [remaining problem rows](https://github.com/DnaCalc/DnaCalc/blob/da3ecc4fb19a3a5529708c311d0e8f05688ac165/docs/generated/problem-functions.md).\n\n", "try-it": "\n`=EXPONDIST(2,0.5,TRUE)` is about `0.632120558828558`: the rate-times-time product is one. About 63.2% of the modeled waits finish within two time units. Changing TRUE to FALSE gives density about `0.183939720585721`.\n\n`=EXPONDIST(0,2,FALSE)` returns `2`. A density can exceed one; it describes probability per unit of time. It is not the probability of a wait lasting exactly zero.\n\n\n", "version-differences": "The recorded environments below distinguish a reading from a same-input comparison. Counts describe captured inputs in each environment; overlapping captures and comparisons are not totals of unique worksheet calls.\n\n| Excel 16.0 build | Platform and CPU | Captured inputs |\n|---|---|---:|\n| 20430 | Windows, 64-bit, CPU not recorded | 9,740 |\n\nThe record contains no same-input comparison between these environments. Reading different inputs on different builds does not establish either a version change or cross-build agreement.\n\n[Recorded environments and comparison details](https://github.com/DnaCalc/ExcelFunctionsHandbook/blob/5dc75391aa5125ccc5abdb095da85950980d6fd8/content/evidence/environments/FUNC.EXPONDIST.json).", "what-it-does": "\n`EXPONDIST(x, lambda, cumulative)` models a nonnegative waiting time at a positive rate `lambda`. TRUE returns the probability of a wait no longer than `x`; FALSE returns a density at `x`. Rate has inverse-time units, so if `x` is in hours, `lambda` is per hour. The mathematical mean wait is `1/lambda`. EXPONDIST is the compatibility spelling.\n\n\n" }, "signature": { "display": "EXPONDIST(x, lambda, cumulative)", "parameters": [ { "description": null, "name": "x", "optional": false, "repeats": false }, { "description": null, "name": "lambda", "optional": false, "repeats": false }, { "description": null, "name": "cumulative", "optional": false, "repeats": false } ], "trailing_repeats": false }, "sources": { "metadata": { "admission": { "label": "implemented", "reason": null }, "arity": { "max": 3, "min": 3 }, "category": "Compatibility", "classification": { "arg_preparation_profile": "ValuesOnlyPreAdapter", "coercion_lift_profile": "Custom", "determinism_class": "Deterministic", "error_collapse_profile": "None", "fec_dependency_profile": "None", "host_interaction_class": "None", "kernel_signature_class": "Custom", "rich_value_usage": "RichBlind", "surface_fec_dependency_profile": "RefOnly", "thread_safety_class": "SafePure", "volatility_class": "NonVolatile" }, "descriptions": { "long": null, "short": "Exponential distribution (older form of EXPON.DIST)", "short_source": "dna-calc-own" }, "docs": { "english_description": "Returns the exponential distribution", "microsoft_url": "https://support.microsoft.com/en-us/office/expondist-function-68ab45fd-cd6d-4887-9770-9357eb8ee06a" }, "entry_kind": "built_in_function", "localized_family_names": null, "localized_names": [ { "locale": "ar-SA", "name": "EXPONDIST" }, { "locale": "bg-BG", "name": "EXPONDIST" }, { "locale": "cs-CZ", "name": "EXPONDIST" }, { "locale": "da-DK", "name": "EKSPFORDELING" }, { "locale": "de-DE", "name": "EXPONDIST" }, { "locale": "el-GR", "name": "EXPONDIST" }, { "locale": "en-AU", "name": "EXPONDIST" }, { "locale": "en-GB", "name": "EXPONDIST" }, { "locale": "en-US", "name": "EXPONDIST" }, { "locale": "es-ES", "name": "DISTR.EXP" }, { "locale": "et-EE", "name": "EXPONDIST" }, { "locale": "fi-FI", "name": "EKSPONENTIAALIJAKAUMA" }, { "locale": "fr-FR", "name": "LOI.EXPONENTIELLE*" }, { "locale": "he-IL", "name": "EXPONDIST" }, { "locale": "hr-HR", "name": "EXPONDIST" }, { "locale": "hu-HU", "name": "EXP.ELOSZLÁS" }, { "locale": "id-ID", "name": "EXPONDIST" }, { "locale": "it-IT", "name": "EXPONDIST" }, { "locale": "ja-JP", "name": "EXPONDIST" }, { "locale": "ko-KR", "name": "EXPONDIST" }, { "locale": "lt-LT", "name": "EXPONDIST" }, { "locale": "lv-LV", "name": "EXPONDIST" }, { "locale": "nb-NO", "name": "EXPONDIST" }, { "locale": "nl-NL", "name": "EXPON.VERD" }, { "locale": "pl-PL", "name": "ROZKŁAD.EXP" }, { "locale": "pt-BR", "name": "EXPONDIST" }, { "locale": "pt-PT", "name": "DISTEXPON" }, { "locale": "ro-RO", "name": "EXPONDIST" }, { "locale": "ru-RU", "name": "ЭКСПРАСП" }, { "locale": "sk-SK", "name": "EXPONDIST" }, { "locale": "sl-SI", "name": "EXPONDIST" }, { "locale": "sr-Latn-RS", "name": "EXPONDIST" }, { "locale": "sv-SE", "name": "EXPONFÖRD" }, { "locale": "th-TH", "name": "EXPONDIST" }, { "locale": "tr-TR", "name": "ÜSTELDAĞ işlevi" }, { "locale": "uk-UA", "name": "EXPONDIST" }, { "locale": "vi-VN", "name": "EXPONDIST" }, { "locale": "zh-CN", "name": "EXPONDIST" }, { "locale": "zh-HK", "name": "EXPONDIST" }, { "locale": "zh-TW", "name": "EXPONDIST" } ], "signature": { "display": "EXPONDIST(x, lambda, cumulative)", "parameters": [ { "description": null, "name": "x", "optional": false, "repeats": false }, { "description": null, "name": "lambda", "optional": false, "repeats": false }, { "description": null, "name": "cumulative", "optional": false, "repeats": false } ], "trailing_repeats": false }, "surface_name": "EXPONDIST", "version_marker": null, "xlcall": { "code": "280", "symbol": "xlfExpondist" } }, "microsoft": "https://support.microsoft.com/en-us/office/expondist-function-68ab45fd-cd6d-4887-9770-9357eb8ee06a" }, "try_it": { "formula": "=EXPONDIST(2,0.5,TRUE)" }, "url": "https://handbook.dnacalc.com/functions/EXPONDIST.html", "variants": [], "versions": [ { "behaviour": "9,740 captured inputs are indexed for this environment. Capture dates: 2026-09-29 to 2026-09-29. This is a reading count, not a comparison with another build.", "excel_build": "16.0 build 20430", "platform": "Windows, 64-bit, CPU not recorded", "sources": [ "https://github.com/DnaCalc/ExcelFunctionsHandbook/blob/5dc75391aa5125ccc5abdb095da85950980d6fd8/content/evidence/environments/FUNC.EXPONDIST.json" ] } ] }