call fftwf_execute_r2r(plan_spectral_to_grid_sin_sin, horzArr%G1, horzArr%G1) does nothing

[brianreinhold]

I am using the FFTW3 interface provided by the MKL. I create plans for R2R transforms at the program start. Later in a time stepping loop, I load a single Asinxsiny spectral component into the two-d array G1 with dimensions G1(4, 8). All elements of G1 are 0 EXCEPT G1(2,2) which has the correct spectral component amplitude. In the debugger I examine G1 after loading. It is correct.

Then I call
call fftwf_execute_r2r(plan_spectral_to_grid_sin_sin, horzArr%G1, horzArr%G1)
and in the debugger I look at the contents of G1. 

IT IS UNCHANGED!!! It is as if the only thing the subroutine did was to return.

[JohnNichols]

There is a note on the FFTW website that you there are problems with Fortran compilers who optimize out the execute module.  You should have a look there and it would be better if you used the MKL Forum on Intel, I mean they have real experts there like @mecej4O