1, ln function is a common mathematical function, and its definition range is {x | x >；; 0}, that is, the input variable of the function value must be greater than zero. This is because the definition of ln function is natural logarithm, that is, logarithm based on E, and E is a natural constant, which is greater than zero, so the domain of ln function can only be positive real number.

2. When using ln function, you need to pay attention to some details and precautions. First of all, the input variable must be a positive real number, and any number less than zero will lead to no definition. Secondly, the input variable cannot be equal to zero, because the logarithm of zero is undefined. In addition, you need to pay attention to some special cases when using ln function. For example, when the input variable is 1, the value of the ln function is equal to 0; When the input variable is e, the value of ln function is equal to 1.

3. When using ln function, we need to pay attention to some mathematical restrictions and conditions. For example, the ln function is continuous in the definition domain, but there is no infinite value. In addition, the ln function monotonically increases in the definition domain, which makes it play an important role in some numerical calculations and statistical analysis.