The OMP_STACKSIZE environment variable indicates the stack
size of threads created by the OpenMP run time. OMP_STACKSIZE sets
the value of the
stacksize-var internal control
variable. OMP_STACKSIZE does not control the stack size of the master
thread. The syntax is as follows:

>>-OMP_STACKSIZE=----size--------------------------------------><
By default, the size value is represented
in Kilobytes. You can also use the suffixes B, K, M, or G if you want
to indicate the size in Bytes, Kilobytes, Megabytes, or Gigabytes
respectively.
White space is allowed between and
around the size value and the suffix. For example, these two examples
both indicate a stack size of 10 Megabytes.
setenv OMP_STACKSIZE 10M
setenv OMP_STACKSIZE " 10 M "
If
OMP_STACKSIZE is not set, the initial value of the
stacksize-var internal
control variable is set to the default value. The default value for
32-bit mode is 256M. For 64-bit mode, the default is up to the limit
imposed by system resources. If the compiler cannot use the stack
size specified or if OMP_STACKSIZE does not conform to the correct
format, the compiler sets the environment variable to
the default value. If the STACK suboption of the XLSMPOPTS environment
variable and the OMP_STACKSIZE environment are specified, the OMP_STACKSIZE
environment variable takes precedence.