search for: dog_dog_

...precision x,y,z z = x+y return end dog2.f: subroutine dogidog(x,y,z) implicit none double precision x,y,z z = x+y return end After bash$ R CMD SHLIB dog1.f bash$ R CMD SHLIB dog2.f note the symbols bash$ nm dog1.so | grep dog 00000730 T dog_dog__ bash$ nm dog2.so | grep dog 00000730 T dogidog_ and in R > x <- 2; y <- 3; z <- 0 > dyn.load("dog1.so") > .Fortran("dog_dog", as.double(x), as.double(y), as.double(z)) Error in .Fortran("dog_dog", as.double(x), as.double(y), as.double(z)) > :...