The OMP_NESTED environment variable enables or disables nested parallelism unless nested parallelism is enabled or disabled by calling the omp_set_nested library routine. If set to TRUE, nested parallelism is enabled; if it is set to FALSE, nested parallelism is disabled. The default value is FALSE.
setenv OMP_NESTED TRUE
omp_set_nested function, see Section 3.1.9 on page 40.