Description
Return eventProbability=-expm1(logSurvival) for a nonpositive finite natural logarithm of survival probability.
Products of small probabilities can round to zero in floating-point arithmetic. Natural logarithms turn products into sums, and centering or expm1-based expressions can reduce avoidable numerical loss. A finite log weight is different from a raw probability and cannot directly represent an exact zero probability.
Return eventProbability=-expm1(logSurvival) for a nonpositive finite natural logarithm of survival probability.
When to use this tool
Use Rare Event Probability Expm1 Crosswalk when you need the stated natural-log contribution or stable conversion between a finite log representation and an ordinary value.
How to use the tool and how it works
- Enter logSurvival. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read eventProbability. Use the output convention below.
Return eventProbability=-expm1(logSurvival) for a nonpositive finite natural logarithm of survival probability.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| logSurvival | Log Survival | Required. Finite number. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| eventProbability | Event Probability | Required. Finite number. |
{
"input": {
"logSurvival": 0
},
"output": {
"eventProbability": 0
}
}Limitations and assumptions
- Using expm1 reduces cancellation near zero. Negative infinity is not accepted, so an exact zero survival probability has no logarithmic input representation here.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Signed zero is exported as zero.
Alternative or Complementary methods
Keep long products or normalizations in the log domain when feasible. Check whether exact zeros need a separate flag and whether the final ordinary-scale result is representable.
References
Similar or alternative tools
- Independent Event Xor Probability
Return first*(1-second)+second*(1-first) for two valid probabilities.
- Log Probability Logsum Two Weights
Set max=max(left,right) and return logSum=max+ln(exp(left-max)+exp(right-max)).