Regarding the unstable function

Hi Tabira,
that's right, if you provide only one decay then WHIZARD applies a BR of 100%. If you provide more decay channels,
then the BR's are determined from the partial widths that WHIZARD calculates for the given decays (at tree level).
In case you still want to redefine the BR's (e.g. according to the ones from the Higgs Cross Section WG), then you
can redefine the integral for the specified decay processes. All of this is documented in sec. 5.8.2 of the manual.
Of course, the integrated cross section is the one of the production process. If you want to have cross sections properly
rescaled to the sigma(production) x BR, then you should/can apply the reweight setting.
Cheers,
    JRR

Thank you for your response. I am trying to find out the partial width for my decay process using: unstable h2 () { ?auto_decays = true } so that I can redefine it for whizard, but I get the error: Mismatch of process and beam setup (scattering/decay). Could it be an issue with my ufo?

output:

?fatal_beam_decay = false
?auto_decays = true
| Creating decay process library for particle h2
| Process library 'default_lib_dp35': initialized
| decay_p35_1: h2 => d1 d1bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_1'
| decay_p35_2: h2 => d1 d2bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_2'
| decay_p35_3: h2 => d1 d3bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_3'
| decay_p35_4: h2 => d1bar d2
| Process library 'default_lib_dp35': recorded process 'decay_p35_4'
| decay_p35_5: h2 => d1bar d3
| Process library 'default_lib_dp35': recorded process 'decay_p35_5'
| decay_p35_6: h2 => u1 u1bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_6'
| decay_p35_7: h2 => u1 u2bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_7'
| decay_p35_8: h2 => u1bar u2
| Process library 'default_lib_dp35': recorded process 'decay_p35_8'
| decay_p35_9: h2 => d2 d2bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_9'
| decay_p35_10: h2 => d2 d3bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_10'
| decay_p35_11: h2 => d2bar d3
| Process library 'default_lib_dp35': recorded process 'decay_p35_11'
| decay_p35_12: h2 => u2 u2bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_12'
| decay_p35_13: h2 => d3 d3bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_13'
| decay_p35_14: h2 => e1 e1bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_14'
| decay_p35_15: h2 => e1 e2bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_15'
| decay_p35_16: h2 => e1 e3bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_16'
| decay_p35_17: h2 => e1bar e2
| Process library 'default_lib_dp35': recorded process 'decay_p35_17'
| decay_p35_18: h2 => e1bar e3
| Process library 'default_lib_dp35': recorded process 'decay_p35_18'
| decay_p35_19: h2 => e2 e2bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_19'
| decay_p35_20: h2 => e2 e3bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_20'
| decay_p35_21: h2 => e2bar e3
| Process library 'default_lib_dp35': recorded process 'decay_p35_21'
| decay_p35_22: h2 => e3 e3bar
| Process library 'default_lib_dp35': recorded process 'decay_p35_22'
| decay_p35_23: h2 => g g
| Process library 'default_lib_dp35': recorded process 'decay_p35_23'
| decay_p35_24: h2 => A A
| Process library 'default_lib_dp35': recorded process 'decay_p35_24'
| decay_p35_25: h2 => Z Ah1
| Process library 'default_lib_dp35': recorded process 'decay_p35_25'
| decay_p35_26: h2 => Wm Hm1
| Process library 'default_lib_dp35': recorded process 'decay_p35_26'
| decay_p35_27: h2 => Wmc Hm1c
| Process library 'default_lib_dp35': recorded process 'decay_p35_27'
| decay_p35_28: h2 => h1 Ah1
| Process library 'default_lib_dp35': recorded process 'decay_p35_28'
| decay_p35_29: h2 => Ah1 Ah1
| Process library 'default_lib_dp35': recorded process 'decay_p35_29'
| decay_p35_30: h2 => Hm1 Hm1c
| Process library 'default_lib_dp35': recorded process 'decay_p35_30'
| decay_p35_31: h2 => a a
| Process library 'default_lib_dp35': recorded process 'decay_p35_31'
| Integrate: current process library needs compilation
| Process library 'default_lib_dp35': compiling ...
| Process library 'default_lib_dp35': keeping makefile
| Process library 'default_lib_dp35': keeping driver
| Process library 'default_lib_dp35': active
| Process library 'default_lib_dp35': ... success.
| Integrate: compilation done
| RNG: Initializing TAO random-number generator
| RNG: Setting seed for random-number generator to 6598
| Initializing integration for process decay_p35_1:
******************************************************************************
******************************************************************************
*** FATAL ERROR: Mismatch of process and beam setup (scattering/decay)
******************************************************************************
******************************************************************************
| There were no errors and 1 warning(s).
WHIZARD run aborted.

I was misunderstanding something but I get it now. I have applied the reweight function and now its working. Thanks a lot for your help!

Hi Tabira,
great that you solved your problem. Just to add a comment, the first problem with the mismatch of scattering/decay was possibly a left-over in your work folder, or this happens sometimes when the unstable statement appears in the SINDARIN input file before the beams statement, where the beams statement would define a scattering.
Cheers,
   JRR