5.9. Calling SPEX from Fortran

5.9.1. Goal

Sometimes you may want to combine SPEX with some of your own code. For instance, you may have a hydrodynamical code calculating the evolution of a cluster of galaxies or a supernova remnant, and you want SPEX to calculate the corresponding spectrum. Or you need to make realistic simulations for a large sample of sources or a broad range of parameters. In that case it can be useful to call SPEX from a fortran program.

5.9.2. Solution

The basic flow of the solution is as follows:

  • Start your fortran program and calculate whatever is needed

  • create a command file for SPEX

  • call SPEX through a system call

  • read the output of SPEX

  • continue with your program

To explain how you can do this, we give below a sample Fortran 90 program. The program first creates a command file called spex.com that contains the input for the run with SPEX. In your case, you can replace the “/opt/spex/bin/spex” to whatever path is appropriate for you to call SPEX. The “<<STOP” is essential for linux to tell when the input stream is finished.

In the command file, it tells how to read the pn spectrum of a cluster of galaxies with roughly metallicity 0.3, temperature 2 keV, redshift 0.01 and Galactic foreground absorption of 10^{24} ~ \mathrm{m}^{-2}. It ignores data at the lowest and highest energies, sets the initial model and parameters for SPEX. It will then perform a fit with SPEX. Next we tell SPEX to open an output file named “spex.out”, that will contain the results of the next part of the SPEX run, an error search on the temperature. Note also that we have set-up the plotting device to “null”, to speed up the calculation (but implying that you do not get to see the fit itself, so use with care). After the error run, we stop SPEX, first by writing the “quit” command for SPEX and then the end of input signal “STOP” for linux. Next we simply close the command file spex.com.

The fortran program then continues by making spex.com executable, and then by executing that file, thereby doing the run with SPEX. When SPEX is finished, fortran takes over control again and reads the spex.out file created by SPEX. The program grabs any info it needs from that file (here the errors on the temperature) and then closes the file.

As a last step, the intermediate outputfile “spex.out” is deleted, as we do not need it longer.

   real nh,z,t
   character*128 s

   z = 0.01    !redshift 0.01
   nh = 1e-4   !1E20 cm**-2 absorption column density (SPEX uses units of 1E28 m**-2)
   t = 2       !temperature 2 keV

   open(unit=12,file='spex.com',status='replace') !open a spex command file called spex.com
   write (12,'("/usr/local/bin/spex <<STOP")')    !call spex
   write (12,'("abu lodders")')                   !set abunances to Lodders scale
   write (s,'("dis ",f6.4," z")') z
   write (12,'(a)') trim(s)                       !write the distance
   write (12,'("data pn pn)')                     !read some spex data set: pn.res & pn.spo
   write (12,'("ign in 1 r 1 1:60")')             !ignore first 60 channels
   write (12,'("ign in 1 12:10000 u kev")')       !ignore E>12 keV region
   write (12,'("com cie")')                       !define a CIE component
   write (12,'("com reds")')                      !define a redshift component
   write (12,'("com abs")')                       !define galactic absorption
   write (12,'("com rel 1 2,3")')                 !couple the components
   write (s,'("par 1 2 z v ",f6.4)') z
   write (12,'(a)') trim(s)                       !set the redshift
   write (s,'("par 1 3 nh v ",1pe12.3)') nh
   write (12,'(a)') trim(s)                       !set the galactic absorption
   write (12,'("par 1 3 nh s f")')                !freeze NH
   write (12,'("par 1 1 06:28 v 0.3")')           !set abundances of C to Ni to 0.3 time solar
   write (s,'("par 1 1 t v ",f5.2)') t
   write (12,'(a)') trim(s)                       !set the temperature
   write (12,'("fit meth cstat")')                !use C-statistics for fitting
   write (12,'("plot dev null")')                 !no visible plots
   write (12,'("plot type data")')                !plot type data
   write (12,'("fit prin 1")')                    !show each fitting step
   write (12,'("fit")')                           !do a fit
   write (12,'("err dchi 1.")')                   !for error search, do Delta chi**2 = 1
   write (12,'("log out spex o")')                !open a file for the SPEX output
                                                  !file will be called "spex.out"
                                                  !the option "o" means overwrite
   write (12,'("err 1 1 t")')                     !do an error search on T
   write (12,'("quit")')                          !done with the spex run, so quit
   write (12,'("STOP")')                          !last command needed to close the command file
   close (12)                                     !close the file spex.com and save

   call system("chmod +x spex.com")               !make file spex.com executable
   call system("spex.com")                        !execute the file spex.com

   open (unit=12,file='spex.out',status='old')    !open the outputfile spex.out
   do k = 1,100000                                !loop over all the lines in this file
     read (12,'(a)',end=20) s                     !read the text of the line; put it in string s
     if (s(2:11).eq."Parameter:") then            !search for the line with text Parameter:
       read (s(34:),*) e1,e2                      !read from this line the errors on T
       err = 0.5 * (-e1 + e2)                     !calculate average pos and neg error
       !..... do further all you wish
   enddo                                          !close loop over lines file spex.out
20 close(12)                                      !close spex.out
   call system("rm spex.out")                     !remove the file spex.out