Block for accessing the external GSL QAG integration routine.
IMPORTANT!!!: The integrand-setup model 'CreateIntegrand' (or a duplicate) must be run before using GSL integration routines or blocks within a larger Modelica model. (Alternatively, one could edit integrand.c directly and then compile "by hand" in a command window:
gcc -fPIC -c integrand.c integration_mi.c
gcc -shared integration.o integration_mi.o -o libgsl_integration_MI.so [.dll for windows])
.GNU_ScientificLibrary.Blocks.integration.QAG_quadrature