code: public static String log(String val) {
          BigDecimal bd;
          try {
              bd = new BigDecimal(val);
              return Math.log(bd.doubleValue()) + "";
          } catch (Exception e) {
              return null;
          }
      }
docs: Returns the natural logarithm (base <i>e</i>) of a {@code double} value.
  
  Any numeric string recognized by {@code BigDecimal} is supported.
  
  @param val A valid number string
  
  @return the value ln&nbsp;{@code a}, the natural logarithm of {@code a}.
  
  @see BigDecimal