C++ Math lgamma()

The lgamma() function computes the logarithm of a gamma function of an argument passed to the function.

Suppose a number is x:

$C++ Math lgamma() function$

Syntax

float lgamma(float x);
double lgamma(double x);
long double lgamma(long double x);
double lgamma(integral x);

Parameter

x: It is a floating point value.

Return value

It returns the logarithm of a gamma function of value x.

Parameter	Return value
x= 1 or x=2	0
x= ±0	+∞
x= -ve integer or ±∞	+∞
x= nan	nan

Example 1

Let's see the simple example when the value of x is 2.

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
     int x=2;
     cout<<"Value of x is : "<<x<<'\n';
     cout<<"lgamma(x) :"<<lgamma(x);
     return 0;
}

Output:

Value of x is : 2
lgamma(x) :0

In the above example, the value of x is 2. Therefore, the function lgamma() returns 0 value.

Example 2

Let's see the simple example when the value of x is 0.

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
     int x=0;
     cout<<"Value of x is : "<<x<<'\n';
     cout<<"lgamma(x) : "<<lgamma(x);
     return 0;
}

Output:

Value of x is : 0
lgamma(x) : inf

In the above example, the value of x is zero. Therefore, the function lgamma() returns +∞.

Example 3

Let's see the simple example when the value of x is a negative integer.

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
     int x= -5;
     cout<<"Value of x is : "<<x<<'\n';
     cout<<"lgamma(x) : "<<lgamma(x);
     return 0;
}

Output:

Value of x is : -5
lgamma(x) : inf

In the above example, the value of x is a negative integer. Therefore, the function lgamma() returns +∞.

Example 4

Let's see the simple example when the value of x is nan.

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
     float x=sqrt(-6);
     cout<<"Value of x is : "<<x<<'\n';
     cout<<"lgamma(x) :"<<lgamma(x);
     return 0;
}

Output: