In C#,
Math.Log() is a Math class method. It is used to return the logarithm of a specified number. This method can be overloaded by changing the number of the arguments passed. There are total 2 methods in the overload list of the
Math.Log() method as follows:
- Math.Log(Double) Method
- Math.Log(Double, Double) Method
Math.Log(Double) Method
This method is used to return the natural (base e) logarithm of a specified number.
Syntax:
public static double Log(double val)
Parameter:
val: It is the specified number whose natural (base e) logarithm to be calculated and its type is System.Double.
Return Value: Returns the natural logarithm of
val and its type is
System.Double.
Note: Parameter
val is always specified as a base 10 number.The return value is depend on the argument passed. Below are some cases:
- If the argument is positive then method will return the natural logarithm or loge(val).
- If the argument is zero, then the result is NegativeInfinity.
- If the argument is Negative(less than zero) or equal to NaN, then the result is NaN.
- If the argument is PositiveInfinity, then the result is PositiveInfinity.
- If the argument is NegativeInfinity, then the result is NaN.
Example:
CSharp
// C# program to demonstrate working
// of Math.Log(Double) method
using System;
class Geeks {
// Main Method
public static void Main(String[] args)
{
// double values whose logarithm
// to be calculated
double a = 4.55;
double b = 0;
double c = -2.45;
double nan = Double.NaN;
double positiveInfinity = Double.PositiveInfinity;
double negativeInfinity = Double.NegativeInfinity;
// Input is positive number so output
// will be logarithm of number
Console.WriteLine(Math.Log(a));
// positive zero as argument, so output
// will be -Infinity
Console.WriteLine(Math.Log(b));
// Input is negative number so output
// will be NaN
Console.WriteLine(Math.Log(c));
// Input is NaN so output
// will be NaN
Console.WriteLine(Math.Log(nan));
// Input is PositiveInfinity so output
// will be Infinity
Console.WriteLine(Math.Log(positiveInfinity));
// Input is NegativeInfinity so output
// will be NaN
Console.WriteLine(Math.Log(negativeInfinity));
}
}
Output:
1.51512723296286
-Infinity
NaN
NaN
Infinity
NaN
Math.Log(Double, Double) Method
This method is used to return the logarithm of a specified number in a specified base.
Syntax:
public static double Log(double val, double base)
Parameter:
val: It is the specified number whose logarithm to be calculated and its type is System.Double.
base: It is the base of the logarithm of type System.Double.
Return Value: It returns the logarithm of
val and its type is
System.Double.
Note: The return value is always depend on the argument passed. Below table depicts the different cases:
| val |
base |
Returned Value |
| val > 0 |
(0 < Base < 1) or(Base > 1) |
logbase(val) |
| val < 0 |
any value |
NaN |
| any value |
base < 0 |
NaN |
| val != 1 |
base = 0 |
NaN |
| val != 1 |
base = +ve Infinity |
NaN |
| val = NaN |
any value |
NaN |
| any value |
base = NaN |
NaN |
| any value |
base = 1 |
NaN |
| val = 0 |
(0 < Base < 1) |
+ve Infinity |
| val = 0 |
base > 1 |
-ve Infinity |
| val = +ve Infinity |
(0 < Base < 1) |
-ve Infinity |
| val = +ve Infinity |
base > 1 |
+ve Infinity |
| val = 1 |
base = 0 |
0 |
| val = 1 |
base = +ve Infinity |
0 |
Example:
CSharp
// C# program to demonstrate working
// of Math.Log(Double, Double) method
using System;
class Geeks {
// Main Method
public static void Main(String[] args)
{
// Here val = 1.3 and base is 0.3 then
// output will be logarithm of given value
Console.WriteLine(Math.Log(1.3, 0.3));
// Here val is 0.5 and base > 1 then output
// will be -0.5
Console.WriteLine(Math.Log(0.5, 4));
// Here val is 0.7 and base = 1 then output
// will be NaN
Console.WriteLine(Math.Log(0.7, 1));
// Here val is 0.7 and base is NaN then output
// will be NaN
Console.WriteLine(Math.Log(0.7, Double.NaN));
}
}
Output:
-0.217915440884381
-0.5
NaN
NaN
References: