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Function `std.math.exponential.log1p`

Calculates the natural logarithm of 1 + x.


						
				real log1p
				(
				

				  real x
				

				) pure nothrow @nogc @safe;
				

				

				double log1p
				(
				

				  double x
				

				) pure nothrow @nogc @safe;
				

				

				float log1p
				(
				

				  float x
				

				) pure nothrow @nogc @safe;

For very small x, log1p(x) will be more accurate than log(1 + x).

Special Values
x	log1p(x)	divide by 0?	invalid?
±0.0	±0.0	no	no
-1.0	-∞	yes	no
<-1.0	-NAN	no	yes
+∞	+∞	no	no

Example

import std.math.traits : isIdentical, isNaN;
import std.math.operations : feqrel;

assert(isIdentical(log1p(0.0), 0.0));
assert(log1p(1.0).feqrel(0.69314) > 16);

writeln(log1p(-1.0)); // -real.infinity
assert(isNaN(log1p(-2.0)));
assert(log1p(real.nan) is real.nan);
assert(log1p(-real.nan) is -real.nan);
writeln(log1p(real.infinity)); // real.infinity

Authors

Walter Bright, Don Clugston, Conversion of CEPHES math library to D by Iain Buclaw and David Nadlinger

License

Boost License 1.0.