数值方法中常遇到的问题，有专门的函数链接库可以使用。IMSL是一套在数值方法上经常被使用的商业函数链接库。Visual Fortran的专业版内含IMSL。

IMSL的函数名称中，第一个字母可以用来判断参数的类型。如果第一个字母是D会使用双精度浮点数来计算并返回答案。第一个字母不是D，则使用单精度浮点数计算。-Numerical methods frequently encountered problems, have a special link library functions can be used. IMSL is a set of numerical methods often used on commercial function link library. Visual Fortran Professional Edition includes the IMSL. IMSL function name, the first letter can be used to determine the type of the parameter. If the first letter is D will be used to calculate the double-precision floating-point number and returns the answer. The first letter is not D, then use the single-precision floating-point calculations.