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#include <math.h>| double | log (double x) |
| long | logl (long double x) |
| float | logf (float x) |
| double | log2 (double x) |
| long | log2l (long double x) |
| float | log2f (float x) |
| double | log10 (double x) |
| long | log10l (long double x) |
| float | log10f (float x) |
| double | log1p (double x) |
| long | log1pl (long double x) |
| float | log1pf (float x) |
Description
The log function computes the value of the natural logarithm of argument x. The log2 function computes the value of the logarithm of argument x to base 2. The log10 function computes the value of the logarithm of argument x to base 10. The log1p function computes the value of
accurately even for very small values of x.
Example:
Example - Logarithm functions
Workings
#include <math.h> #include <stdio.h> int main() { printf("\n x \t log \t log2 \t log10 \t log1p"); for(double x=0; x<=10; x+=0.5) printf("\n%lf\t%lf\t%lf\t%lf\t%lf", x, log(x), log2(x), log10(x), log1p(x)); return 0; }
Solution
Output
x log log2 log10 log1p 0.000000 -inf -inf -inf 0.000000 0.500000 -0.693147 -1.000000 -0.301030 0.405465 1.000000 0.000000 0.000000 0.000000 0.693147 1.500000 0.405465 0.584963 0.176091 0.916291 2.000000 0.693147 1.000000 0.301030 1.098612 2.500000 0.916291 1.321928 0.397940 1.252763 3.000000 1.098612 1.584963 0.477121 1.386294 3.500000 1.252763 1.807355 0.544068 1.504077 4.000000 1.386294 2.000000 0.602060 1.609438 4.500000 1.504077 2.169925 0.653213 1.704748 5.000000 1.609438 2.321928 0.698970 1.791759 5.500000 1.704748 2.459432 0.740363 1.871802 6.000000 1.791759 2.584963 0.778151 1.945910 6.500000 1.871802 2.700440 0.812913 2.014903 7.000000 1.945910 2.807355 0.845098 2.079442 7.500000 2.014903 2.906891 0.875061 2.140066 8.000000 2.079442 3.000000 0.903090 2.197225 8.500000 2.140066 3.087463 0.929419 2.251292 9.000000 2.197225 3.169925 0.954243 2.302585 9.500000 2.251292 3.247928 0.977724 2.351375 10.000000 2.302585 3.321928 1.000000 2.397895
Special Values
log ( ±0 ), log2 ( ±0 ), and log10( ±0 ) return -∞ and raise the divide-by-zero floating-point exception. log ( 1 ), log2 ( 1 ), and log10 ( 1 ) return +0. log ( x ), log2 ( x ), and log10 ( x ) return a NaN and raise the invalid floating-point exception for x < 0. log ( +∞ ), log2 ( +∞ ), and log10 ( +∞ ) return +∞. log1p ( ±0 ) returns ±0. log1p ( -1 ) returns -∞ and raises the divide-by-zero floating-point exception. log1p ( x ) returns a NaN and raises the invalid floating-point exception for x < -1. log1p ( +∞ ) returns +∞.
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