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*AIX Version 4 Files Reference*

## math.h File

### Purpose

Defines math subroutines and constants.

### Description

The **/usr/include/math.h** header file contains declarations
of all the subroutines in the Math library (**libm.a**) and of various subroutines in the Standard C
Library (**libc.a**) that return floating-point values.

Among other things, the** math.h** file defines the following macro,
which is used as an error-return value:

**HUGE_VAL** |
Specifies the maximum value of a double-precision floating-point number: +infinity on
machines that support IEEE-754 and **DBL_MAX** otherwise. |

If you define the **__MATH__** preprocessor variable before
including the **math.h **file, the **math.h** file defines macros that make the names of certain
math subroutines appear to the compiler as** __***xxxx*. The following names are redefined to
have the __ (double underscore) prefix:

**exp** |
sin |

**asin** |
log |

**cos** |
acos |

**log10** |
tan |

**atan** |
sqrt |

**fabs** |
atan2 |

These special names instruct the C compiler to generate code that
avoids the overhead of the Math library subroutines and issues compatible-mode floating-point
subroutines directly. The **__MATH__ ** variable is defined by default.

If **_XOPEN_SOURCE** variable is defined, the following mathematical
constants are defined for your convenience. The values are of type double and are accurate to the
precision of this type. That is, the machine value is the mathematical value rounded to double
precision.

**M_E** |
Base of natural logarithms (*e*) |

**M_LOG2E** |
Base-2 logarithm of *e* |

**M_LOG10E** |
Base-10 logarithm of *e* |

**M_LN2** |
Natural logarithm of 2 |

**M_LN10** |
Natural logarithm of 10 |

**M_PI** |
Pi, the ratio of the circumference of a circle to its diameter |

**M_PI_2** |
Value of pi divided by 2 |

**M_PI_4** |
Value of pi divided by 4 |

**M_1_PI** |
Value of 1 divided by pi |

**M_2_PI** |
Value of 2 divided by pi |

**M_2_SQRTPI** |
Value of 2 divided by the positive square root of pi |

**M_SQRT2** |
Positive square root of 2 |

**M_SQRT1_2** |
Positive square root of 1/2 |

### Related Information

The **values.h** file.

Header Files
Overview defines header files, describes how they are used, and lists several of the header files
for which information is provided in this documentation.

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