$log()

Synopsis

$log(<number>)

Technical

Returns the natural logarithm of <number>: the value x such that exp(x) equals the input. The real-valued domain is positive numbers. See exp for the inverse operation and log10 for base-ten logarithms.

The first function argument is converted with atof, accepting decimal fractions and scientific notation. Additional arguments are ignored. Missing input returns the empty string. Nonnumeric text converts to zero, and a numeric prefix can be accepted despite trailing text.

The calculation uses the C library's log and a C double. Results are formatted with %.50g, not limited to six decimal places. The floating_point_math and floating_point_precision settings do not affect the calculation or formatting. Extra displayed digits do not imply 50 digits of accuracy.

Returns and restrictions

A calculated number when the library leaves errno at zero. A reported EDOM becomes DOM, ERANGE becomes RANGE, and another reported error becomes the empty string. The wrapper clears errno after argument conversion and before calculating.

Negative inputs produce a domain error; zero is a logarithmic pole. Error signaling can use errno or floating-point exception flags, but EPIC checks only errno. Consequently, invalid inputs can return library values such as NaN or negative infinity instead of DOM or RANGE on platforms that report only through exception flags. Positive infinity and NaN inputs ordinarily produce infinity and NaN, respectively. These are C-library behaviors; see the ISO C draft's math-library specification.

This function calculates a logarithm; it does not control logging. See the log command for log destinations.

Examples

The approximate examples describe numeric values; returned strings may contain more digits.

Source

Registration, MATH_FUNCTION, and MATH_RETVAL are in source/functions.c. Argument conversion and floating-point return formatting are in include/functions.h.