Setting the Default Mode of Vector Math with an Environment Variable

Intel® Math Kernel Library (Intel® MKL) enables overriding the default setting of the Vector Mathematics (VM) global mode using the MKL_VML_MODE environment variable.

Because the mode is set or can be changed in different ways, their precedence determines the actual mode used. The settings and function calls that set or change the VM mode are listed below, with the precedence growing from lowest to highest:

  1. The default setting
  2. The MKL_VML_MODE environment variable
  3. A call vmlSetMode function
  4. A call to any VM function other than a service function

For more details, see the Vector Mathematical Functions section in the Intel MKL Developer Reference and the description of the vmlSetMode function in particular.

To set the MKL_VML_MODE environment variable, use the following command in your command shell:

  • For the bash shell:

    export MKL_VML_MODE=<mode-string>

  • For a C shell (csh or tcsh):

    setenv MKL_VML_MODE <mode-string>

In these commands, <mode-string> controls error handling behavior and computation accuracy, consists of one or several comma-separated values of the mode parameter listed in the table below, and meets these requirements:

  • Not more than one accuracy control value is permitted
  • Any combination of error control values except VML_ERRMODE_DEFAULT is permitted
  • No denormalized numbers control values are permitted
Values of the mode Parameter
Value of mode Description
Accuracy Control
VML_HA high accuracy versions of VM functions
VML_LA low accuracy versions of VM functions
VML_EP enhanced performance accuracy versions of VM functions
Denormalized Numbers Handling Control
VML_FTZDAZ_ON Faster processing of denormalized inputs is enabled.
VML_FTZDAZ_OFF Faster processing of denormalized inputs is disabled.
Error Mode Control
VML_ERRMODE_IGNORE On computation error, VM Error status is updated, but otherwise no action is set. Cannot be combined with other VML_ERRMODE settings.
VML_ERRMODE_NOERR On computation error, VM Error status is not updated and no action is set. Cannot be combined with other VML_ERRMODE settings.
VML_ERRMODE_STDERR On error, the error text information is written to stderr.
VML_ERRMODE_EXCEPT On error, an exception is raised.
VML_ERRMODE_CALLBACK On error, an additional error handler function is called.
VML_ERRMODE_DEFAULT On error, an exception is raised and an additional error handler function is called.

These commands provide an example of valid settings for the MKL_VML_MODE environment variable in your command shell:

  • For the bash shell:

    export MKL_VML_MODE=VML_LA,VML_ERRMODE_ERRNO,VML_ERRMODE_STDERR

  • For a C shell (csh or tcsh):

    setenv MKL_VML_MODE VML_LA,VML_ERRMODE_ERRNO,VML_ERRMODE_STDERR

Note

VM ignores the MKL_VML_MODE environment variable in the case of incorrect or misspelled settings of mode.

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