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Exponential, Gamma, and Weibull Waiting-Time Models

Install and import#

bash
npm install fintech-algorithms
ts
import { exponentialGammaAndWeibullWaitingTimeModels } from "fintech-algorithms/foundations/probability-distributions-and-simulation-basics/exponential-gamma-and-weibull-waiting-time-models";

Signature#

exponentialGammaAndWeibullWaitingTimeModels(input)

Evaluates three waiting-time models at the same point input.x: the exponential survival function, the gamma density, and the Weibull survival function, all sharing shape and scale.

Parameters#

NameTypeNotes
inputD00InputOne record carrying x (the waiting time to evaluate), shape (the gamma and Weibull shape parameter) and scale (the common scale), plus p and sigma, which the family entry point validates before dispatching.
sigma: strictly positive · p: between 0 and 1 inclusive

Returns#

D00Output

An object with exponentialSurvival (probability of waiting longer than x under an exponential with mean scale), gammaPdf (the gamma density at x) and weibullSurvival (the Weibull survival at x).

Errors#

  • When p is missing or outside 0 to 1 — this check runs for every topic in the family — throws RangeError
  • When sigma is zero or negative — this check runs for every topic from A05 onward — throws RangeError

Complexity: time O(1), space O(1).

Worked example#

verified This is the worked example published in the article, replayed by the test suite on every run. The output cannot drift.

Input#

input
{
  "values": [0.2, 0.5, 0.7, 1, 1.4],
  "x": 1,
  "p": 0.3,
  "n": 5,
  "k": 2,
  "lambda": 2,
  "seed": 42,
  "sampleCount": 8,
  "mu": 0,
  "sigma": 1,
  "df": 5,
  "shape": 2,
  "scale": 1.5,
  "components": [
    {
      "weight": 0.7,
      "mean": 0,
      "sd": 1
    },
    {
      "weight": 0.3,
      "mean": 3,
      "sd": 0.8
    }
  ]
}

Call#

exponentialGammaAndWeibullWaitingTimeModels(input)

Returns#

object with 2 fields: exponentialSurvival, gammaPdf

{
  "exponentialSurvival": 0.513417119032592,
  "gammaPdf": 0.22818538623670756
}

Diagrams#

Exponential, Gamma, and Weibull Waiting-Time Models — article hero
Exponential, Gamma, and Weibull Waiting-Time Models — calculation ledger
Exponential, Gamma, and Weibull Waiting-Time Models — concept anatomy
Exponential, Gamma, and Weibull Waiting-Time Models — failure boundary
Exponential, Gamma, and Weibull Waiting-Time Models — method map
Exponential, Gamma, and Weibull Waiting-Time Models — scenario contrast

How it works#

This page states the contract — how to call it correctly. The article explains the concept: why it works, and where it breaks.

Read the article →

References#

The rest of the Probability Distributions and Simulation Basics family#