docs-v2/content/flux/v0/stdlib/math/ldexp.md

title	description	menu	weight
math.ldexp() function	`math.ldexp()` is the inverse of `math.frexp()`. It returns `frac x 2**exp`.	flux_v0_ref name parent identifier math.ldexp math math/ldexp	101

math.ldexp() is the inverse of math.frexp(). It returns frac x 2**exp.

Function type signature

(exp: int, frac: float) => float

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Parameters

frac

({{< req >}}) Fraction to use in the operation.

exp

({{< req >}}) Exponent to use in the operation.

Examples

• Return the inverse of math.frexp
• Use math.ldexp in map

Return the inverse of math.frexp

import "math"

math.ldexp(frac: 0.5, exp: 6)// 32.0

Use math.ldexp in map

import "math"

data
    |> map(fn: (r) => ({_time: r._time, tag: r.tag, _value: math.ldexp(frac: r.frac, exp: r.exp)}))

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Input data

*tag	_time	exp	frac
t1	2021-01-01T00:00:00Z	2	-0.545
t1	2021-01-01T00:00:10Z	4	0.6825
t1	2021-01-01T00:00:20Z	3	0.91875
t1	2021-01-01T00:00:30Z	5	0.5478125
t1	2021-01-01T00:00:40Z	4	0.951875
t1	2021-01-01T00:00:50Z	3	0.55375

*tag	_time	exp	frac
t2	2021-01-01T00:00:00Z	5	0.6203125
t2	2021-01-01T00:00:10Z	3	0.62125
t2	2021-01-01T00:00:20Z	2	-0.9375
t2	2021-01-01T00:00:30Z	5	0.6178125
t2	2021-01-01T00:00:40Z	4	0.86625
t2	2021-01-01T00:00:50Z	1	0.93

Output data

_time	_value	*tag
2021-01-01T00:00:00Z	-2.18	t1
2021-01-01T00:00:10Z	10.92	t1
2021-01-01T00:00:20Z	7.35	t1
2021-01-01T00:00:30Z	17.53	t1
2021-01-01T00:00:40Z	15.23	t1
2021-01-01T00:00:50Z	4.43	t1

_time	_value	*tag
2021-01-01T00:00:00Z	19.85	t2
2021-01-01T00:00:10Z	4.97	t2
2021-01-01T00:00:20Z	-3.75	t2
2021-01-01T00:00:30Z	19.77	t2
2021-01-01T00:00:40Z	13.86	t2
2021-01-01T00:00:50Z	1.86	t2

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