log function
double log(Converts x to a double and returns the natural logarithm of the value.
Returns negative infinity if x is equal to zero. Returns NaN if x is NaN or less than zero.
Source
external double log(num x);
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dartlang.org/stable/1.24.3/dart-math/log.html