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# Python math library | expm1() method

• Last Updated : 31 Oct, 2018

Python has math library and has many functions regarding to it. One such function is `expm1()`. This function mathematically computes the value of `exp(x) - 1`. This method can be used if we need to compute this very value.

Syntax : math.expm1()

Parameters :
x : Number whose exp(x)-1 has to be computed.

Returns : Returns the computed value of “exp(x)-1”

Code #1 : Demonstrate the working of expm1()

 `# Python3 code to demonstrate``# the working of expm1()``import` `math`` ` `# initializing the value ``test_int ``=` `4``test_neg_int ``=` `-``3`` ` `# checking expm1() values``# doesn't throw error with negative``print` `(``"The expm1 value using positive integer : "``                      ``+` `str``(math.expm1(test_int)))``                       ` `print` `(``"The expm1 value using negative integer : "``                  ``+` `str``(math.expm1(test_neg_int)))`

Output :

```The expm1 value using positive integer : 53.598150033144236
The expm1 value using negative integer : -0.950212931632136```

“exp() – 1” vs “expm1()”

There would be a question why `expm1()` method was even created if we could always compute exp() and then subtract 1 from it. The first reason is that value `exp() - 1` is used a lot in mathematics and science applications and formulas.
The most important reason is that for smaller value of x, of the order less than e-10, `expm1()` method give a result more accurate than `exp() - 1`.

Code #2 : Comparing expm1() and exp()-1

 `# Python3 code to demonstrate``# the application of expm1()``import` `math`` ` `# initializing the value ``test_int ``=` `1e``-``10`` ` `# checking expm1() values``# expm1() is more accurate``print` `(``"The value with exp()-1  : "` `+` `str``(math.exp(test_int)``-``1``))``print` `(``"The value with expm1() : "` `+` `str``(math.expm1(test_int)))`

Output :

```The value with exp()-1  : 1.000000082740371e-10
The value with expm1() : 1.00000000005e-10
```

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