Intel(R) Math Kernel Library for Linux* OS User's Guide

6 Intel® Math Kernel Library User’s GuideExample 6-1Changing the Number of Threads (continued)CALL OMP_SET_NUM_THREADS(2);DO I=1,NDO J=1,NA(I,J) = I+JB(I,J) = I*jC(I,J) = 0.0END DOEND DOCALL DGEMM('N','N',N,N,N,ALPHA,A,N,B,N,BETA,C,N)print *,'Row A C'DO i=1,10write(*,'(I4,F20.8,F20.8)') I, A(1,I),C(1,I)END DOSTOPENDUsing Additional Threading ControlIntel MKL provides optional threading controls, that is, the environment variables andservice functions that are independent of OpenMP. They behave similar to their OpenMPequivalents, but take precedence over them in the meaning that the MKL-specific threadingcontrols are inspected first. By using these controls along with OpenMP variables, you canthread the part of the application that does not call Intel MKL and the library independentlyfrom each other.These controls enable you to specify the number of threads for Intel MKL independently ofthe OpenMP settings. Although Intel MKL may actually use a different number of threadsfrom the number suggested, the controls will also enable you to instruct the library to tryusing the suggested number when the number used in the calling application isunavailable.NOTE. Intel MKL does not always have a choice on the number ofthreads for certain reasons, such as system resources.Use of the Intel MKL threading controls in your application is optional. If you do not usethem, the library will mainly behave the same way as Intel MKL 9.1 in what relates tothreading with the possible exception of a different default number of threads.6-8