In Fortran, I have an 1D array of type real, real :: work(2*N), which represents N complex numbers. I don't have any impact of the declaration of the array.
Later I need to apply a complex conjugation on work. However, conjg(work(:)) does not work since it is of type real.
Is there a efficient way to convince the compiler to apply the conjg to my array?
The easiest approach is already in the comment by HighPerformanceMark, just multiply the elements representing the imaginary part by -1.
You can also use equivalence between a real array and a complex array. It will be just one array but viewed as both real and complex. Maybe not strictly standard conforming (not sure) but working as long as N is constant.
The equivalence is used as:
real :: work(2*N)
complex :: cwork(N)
!both work and cwork point to the same data
equivalence (work, cwork)
work = some_initial_value
!this conjugates work at the same time as cwork because they are just different names for the same array
cwork = conjg(cwork)