Calculates the natural logarithm of the sum of field value and 1. For small values of x, the result of log1p(x) is much closer to the true result of ln(1 + x) than the floating-point evaluation of log(1.0+x).

Note

Math functions on ARM architecture may return different results in very high-precision calculationsc compared to Intel/AMD architectures.

ParameterTypeRequiredDefault ValueDescription
asstringoptional[a] _log1p The name of the output field.
field[b]stringrequired   The name of the input field.

[a] Optional parameters use their default value unless explicitly set.

[b] The parameter name field can be omitted.

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math:log1p() Examples

Click + next to an example below to get the full details.

Calculate Natural Logarithm of Value Plus One

Calculate the natural logarithm of (1 + x) using the math:log1p() function

Query
logscale
x := 0.0001
        | math:log1p(x, as=log1p_result)
Introduction

In this example, the math:log1p() function is used to demonstrate accurate calculation of ln(1 + x), particularly for small values where standard floating-point arithmetic might lose precision.

Step-by-Step

  1. Starting with the source repository events.

  2. logscale
    x := 0.0001

    Assigns a small value 0.0001 to a field named x. This demonstrates the function's precision advantage with small values.

  3. logscale
    | math:log1p(x, as=log1p_result)

    Calculates ln(1 + x) for the value in field x and returns the result in a new field named log1p_result. If the as parameter is not specified, the result is returned in a field named _log1p as default.

  4. Event Result set.

Summary and Results

The query is used to calculate ln(1 + x) with high precision, particularly beneficial for small values where standard floating-point calculations might be inaccurate.

This query is useful, for example, when working with small incremental changes, calculating precise logarithmic values near 1, or in financial calculations involving rates close to zero.

Sample output from the incoming example data:

log1p_result
0.00009999999833333334

The result demonstrates the precise calculation of ln(1 + 0.0001). Note that for very small values, the result is close to, but not exactly equal to, the input value. This is because math:log1p() provides better numerical accuracy than calculating ln(1.0 + x) directly, especially important when working with small values where floating-point precision matters.