# fimf-max-error, Qimf-max-error

Defines the maximum allowable relative error for math library function results, including division and square root.

## Syntax

Linux: | -fimf-max-error=ulps[:funclist]

macOS: | -fimf-max-error=ulps[:funclist]

Windows: | /Qimf-max-error:ulps[:funclist]

Optional argument funclist is not supported for ifx.

## Arguments

ulps | Is a positive, floating-point number indicating the maximum allowable relative error the compiler should use. The format for the number is [digits] [.digits] [ { e | E }[sign]digits].
funclist | Is an optional list of one or more math library functions to which the attribute should be applied. Do not specify the standard Fortran name of the math function; you must specify the actual math library name. If you specify more than one function, they must be separated with commas. Precision-specific variants like sin and sinf are considered different functions, so you would need to use -fimf-max-error=4.0:sin,sinf (or /Qimf-max-error=4.0:sin,sinf) to specify the maximum allowable relative error for both the single-precision and double-precision sine functions. You also can specify the symbol /f to denote single-precision divides, symbol / to denote double-precision divides, symbol /l to denote extended-precision divides, and symbol /q to denote quad-precision divides. For example you can specify -fimf-max-error=4.0:/ or /Qimf-max-error:4.0:/.

## Default

-fimf-precision=medium or /Qimf-precision:medium | The compiler uses medium precision when calling math library functions. Note that other options can affect precision; see below for details.

## Description

This option defines the maximum allowable relative error, measured in ulps, for math library function results.

This option can affect run-time performance and the accuracy of results.

If you need to define the accuracy for a math function of a certain precision, specify the function name of the precision that you need. For example, if you want double precision, you can specify :sin; if you want single precision, you can specify :sinf, as in -fimf-max-error=4.0:sin or /Qimf-max-error:4.0:sin, or -fimf-max-error=4.0:sqrtf or /Qimf-max-error:4.0:sqrtf.

If you do not specify any function names, then the setting applies to all functions (and to all precisions). However, as soon as you specify an individual function name, the setting applies only to the function of corresponding precision. So, for example, sinf applies only to the single-precision sine function, sin applies only to the double-precision sine function, sinl applies only to the extended-precision sine function, etc.

There are three options you can use to express the maximum relative error. They are as follows:

Linux and macOS

- -fimf-precision

- -fimf-max-error

- -fimf-accuracy-bits

Windows

- /Qimf-precision

- /Qimf-max-error

- /Qimf-accuracy-bits

If more than one of these options are specified, the default value for the maximum relative error is determined by the last one specified on the command line.

If none of the above options are specified, the default values for the maximum relative error are determined by the setting of the following options:

- [Q]fast-transcendentals (ifort only)

- [Q]prec-div (ifort only)

- [Q]prec-sqrt (ifort only)

- -fp-model (Linux and macOS) or /fp (Windows)

### Note

Many routines in libraries LIBM (Math Library) and SVML (Short Vector Math Library) are more highly optimized for Intel® microprocessors than for non-Intel microprocessors.

### Note

The standard Fortran names for the various math intrinsic functions do not match the math library names of the math intrinsic functions. You must find the actual math library name that is generated for the relevant Fortran math intrinsic.

One way to do this is to generate assembly code by using one of the following options:

Linux and macOS

-S

Windows

/Fa or /S

The assembly code will show the actual math library name.

For example, if you create a program that contains a call to SIN(x) where x is declared as REAL(KIND=4) and then use option S to produce assembly code for the program, the assembly code will show a call to sinf.

To define the maximum allowable relative error for the single-precision sine function, you should specify:

Linux and macOS

-fimf-max-error=sinf

Windows

/Qimf-max-error:sinf

### Note

This option only applies to host compilation. When offloading is enabled, it does not impact device-specific compilation. Offloading can only be enabled when using ifx.

Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex. Notice revision #20201201

## IDE Equivalent

None

## Alternate Options

None

Parent topic: Floating-Point Options

## See Also

fimf-absolute-error, Qimf-absolute-error compiler option
fimf-accuracy-bits, Qimf-accuracy-bits compiler option
fimf-arch-consistency, Qimf-arch-consistency compiler option
fimf-domain-exclusion, Qimf-domain-exclusion compiler option
fimf-precision, Qimf-precision compiler option
fimf-use-svml_Qimf-use-svml compiler option