# Math.Exp Method (Double)

.NET Framework (current version)

Returns e raised to the specified power.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

## Syntax

```public static double Exp(
double d
)
```

#### Parameters

d
Type: System.Double

A number specifying a power.

#### Return Value

Type: System.Double

The number e raised to the power d. If d equals NaN or PositiveInfinity, that value is returned. If d equals NegativeInfinity, 0 is returned.

## Remarks

e is a mathematical constant whose value is approximately 2.71828.

Use the Pow method to calculate powers of other bases.

Exp is the inverse of Log.

## Examples

The following example uses Exp to evaluate certain exponential and logarithmic identities for selected values.

```// Example for the Math.Exp( double ) method.
using System;

class ExpDemo
{
public static void Main()
{
Console.WriteLine(
"This example of Math.Exp( double ) " +
"generates the following output.\n" );
Console.WriteLine(
"Evaluate [e ^ ln(X) == ln(e ^ X) == X] " +
"with selected values for X:" );

UseLnExp(0.1);
UseLnExp(1.2);
UseLnExp(4.9);
UseLnExp(9.9);

Console.WriteLine(
"\nEvaluate these identities with " +
"selected values for X and Y:" );
Console.WriteLine( "   (e ^ X) * (e ^ Y) == e ^ (X + Y)" );
Console.WriteLine( "   (e ^ X) ^ Y == e ^ (X * Y)" );
Console.WriteLine( "   X ^ Y == e ^ (Y * ln(X))" );

UseTwoArgs(0.1, 1.2);
UseTwoArgs(1.2, 4.9);
UseTwoArgs(4.9, 9.9);
}

// Evaluate logarithmic/exponential identity with a given argument.
static void UseLnExp(double arg)
{
// Evaluate e ^ ln(X) == ln(e ^ X) == X.
Console.WriteLine(
"\n      Math.Exp(Math.Log({0})) == {1:E16}\n" +
"      Math.Log(Math.Exp({0})) == {2:E16}",
arg, Math.Exp(Math.Log(arg)), Math.Log(Math.Exp(arg)) );
}

// Evaluate exponential identities that are functions of two arguments.
static void UseTwoArgs(double argX, double argY)
{
// Evaluate (e ^ X) * (e ^ Y) == e ^ (X + Y).
Console.WriteLine(
"\nMath.Exp({0}) * Math.Exp({1}) == {2:E16}" +
"\n          Math.Exp({0} + {1}) == {3:E16}",
argX, argY, Math.Exp(argX) * Math.Exp(argY),
Math.Exp(argX + argY) );

// Evaluate (e ^ X) ^ Y == e ^ (X * Y).
Console.WriteLine(
" Math.Pow(Math.Exp({0}), {1}) == {2:E16}" +
"\n          Math.Exp({0} * {1}) == {3:E16}",
argX, argY, Math.Pow(Math.Exp(argX), argY),
Math.Exp(argX * argY) );

// Evaluate X ^ Y == e ^ (Y * ln(X)).
Console.WriteLine(
"           Math.Pow({0}, {1}) == {2:E16}" +
"\nMath.Exp({1} * Math.Log({0})) == {3:E16}",
argX, argY, Math.Pow(argX, argY),
Math.Exp(argY * Math.Log(argX)) );
}
}

/*
This example of Math.Exp( double ) generates the following output.

Evaluate [e ^ ln(X) == ln(e ^ X) == X] with selected values for X:

Math.Exp(Math.Log(0.1)) == 1.0000000000000001E-001
Math.Log(Math.Exp(0.1)) == 1.0000000000000008E-001

Math.Exp(Math.Log(1.2)) == 1.2000000000000000E+000
Math.Log(Math.Exp(1.2)) == 1.2000000000000000E+000

Math.Exp(Math.Log(4.9)) == 4.9000000000000012E+000
Math.Log(Math.Exp(4.9)) == 4.9000000000000004E+000

Math.Exp(Math.Log(9.9)) == 9.9000000000000004E+000
Math.Log(Math.Exp(9.9)) == 9.9000000000000004E+000

Evaluate these identities with selected values for X and Y:
(e ^ X) * (e ^ Y) == e ^ (X + Y)
(e ^ X) ^ Y == e ^ (X * Y)
X ^ Y == e ^ (Y * ln(X))

Math.Exp(0.1) * Math.Exp(1.2) == 3.6692966676192444E+000
Math.Exp(0.1 + 1.2) == 3.6692966676192444E+000
Math.Pow(Math.Exp(0.1), 1.2) == 1.1274968515793757E+000
Math.Exp(0.1 * 1.2) == 1.1274968515793757E+000
Math.Pow(0.1, 1.2) == 6.3095734448019331E-002
Math.Exp(1.2 * Math.Log(0.1)) == 6.3095734448019344E-002

Math.Exp(1.2) * Math.Exp(4.9) == 4.4585777008251705E+002
Math.Exp(1.2 + 4.9) == 4.4585777008251716E+002
Math.Pow(Math.Exp(1.2), 4.9) == 3.5780924170885260E+002
Math.Exp(1.2 * 4.9) == 3.5780924170885277E+002
Math.Pow(1.2, 4.9) == 2.4433636334442981E+000
Math.Exp(4.9 * Math.Log(1.2)) == 2.4433636334442981E+000

Math.Exp(4.9) * Math.Exp(9.9) == 2.6764450551890982E+006
Math.Exp(4.9 + 9.9) == 2.6764450551891015E+006
Math.Pow(Math.Exp(4.9), 9.9) == 1.1684908531676833E+021
Math.Exp(4.9 * 9.9) == 1.1684908531676829E+021
Math.Pow(4.9, 9.9) == 6.8067718210957060E+006
Math.Exp(9.9 * Math.Log(4.9)) == 6.8067718210956985E+006
*/
```

## Version Information

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1