• Introduction
• ANSI C vs. Non-ANSI C and IMSL.h
• Matrix Storage Modes for the MATH and STAT Libraries
• Memory Allocation for Output Arrays
• Finding the Right Function
• Organization of the Documentation
• Naming Conventions
• Error Handling, Underflow and Overflow
• Printing Results
• Missing Values
• Complex Arithmetic

Many functions return a pointer to an array containing the computed answers. If the function invocation uses the optional arguments

IMSL_RETURN_USER, float a[ ]

the computed answers are stored in the user-provided array a, and the pointer returned by the function is set to point to the user-provided array a. If an invocation does not use IMSL_RETURN_USER, the function initializes the pointer (through a memory allocation request to malloc) and stores the answers there. (To release this space, free can be used. Both malloc and free are standard C library functions declared in the header <stdlib.h>.) In this way, the allocation of space for the computed answers can be made either by the user or internally by the function.

Similarly, other optional arguments specify whether additional computed output arrays are allocated by the user or are to be allocated internally by the function. For example, in many functions in "Linear Systems," the optional arguments

IMSL_INVERSE_USER, float inva[]   (Output)
IMSL_INVERSE, float **p_inva   (Output)

specify two mutually exclusive optional arguments. If the first option is chosen, the inverse of the matrix is stored in the user-provided array inva. In the second option, float **p_inva refers to the address of a pointer to the inverse. If the second option is chosen, on return the pointer is initialized (through a memory allocation request to malloc), and the inverse of the matrix is stored there. Typically, float *p_inva is declared, &p_inva is used as an argument to this function and free(p_inva) is used to release the space.