set_parameters Subroutine

    subroutine set_parameters(me,n,fcn,solout,iprint,nstiff,nmax,hinitial,&
                              hmax,safe,fac1,fac2,beta,icomp,status_ok)

    implicit none

    class(dop853_class),intent(inout)        :: me
    integer,intent(in)                       :: n         !! the dimension of the system (size of \(y\) and \(y'\) vectors)
    procedure(deriv_func)                    :: fcn       !! subroutine computing the value of \( y' = f(x,y) \)
    procedure(solout_func),optional          :: solout    !! subroutine providing the
                                                          !! numerical solution during integration.
                                                          !! if `iout>=1`, it is called during integration.
                                                          !! supply a dummy subroutine if `iout=0`.
    integer,intent(in),optional              :: iprint    !! switch for printing error messages
                                                          !! if `iprint==0` no messages are being printed
                                                          !! if `iprint/=0` messages are printed with
                                                          !! `write (iprint,*)` ...
    integer,intent(in),optional              :: nstiff    !! test for stiffness is activated after step number
                                                          !! `j*nstiff` (`j` integer), provided `nstiff>0`.
                                                          !! for negative `nstiff` the stiffness test is
                                                          !! never activated.
    integer,intent(in),optional              :: nmax      !! the maximal number of allowed steps.
    real(wp),intent(in),optional             :: hinitial  !! initial step size, for `hinitial=0` an initial guess
                                                          !! is computed with help of the function [[hinit]].
    real(wp),intent(in),optional             :: hmax      !! maximal step size, defaults to `xend-x` if `hmax=0`.
    real(wp),intent(in),optional             :: safe      !! safety factor in step size prediction
    real(wp),intent(in),optional             :: fac1      !! parameter for step size selection.
                                                          !! the new step size is chosen subject to the restriction
                                                          !! `fac1 <= hnew/hold <= fac2`
    real(wp),intent(in),optional             :: fac2      !! parameter for step size selection.
                                                          !! the new step size is chosen subject to the restriction
                                                          !! `fac1 <= hnew/hold <= fac2`
    real(wp),intent(in),optional             :: beta      !! is the `beta` for stabilized step size control
                                                          !! (see section iv.2). positive values of `beta` ( <= 0.04 )
                                                          !! make the step size control more stable.
    integer,dimension(:),intent(in),optional :: icomp     !! the components for which dense output is required (size from 0 to `n`).
    logical,intent(out)                      :: status_ok !! will be false for invalid inputs.

    call me%destroy()

    status_ok = .true.

    !required inputs:
    me%n = n
    me%fcn => fcn

    !optional inputs:

    if (present(solout)) me%solout => solout

    if (present(iprint))   me%iprint   = iprint
    if (present(nstiff))   me%nstiff   = nstiff
    if (present(hinitial)) me%hinitial = hinitial
    if (present(hmax))     me%hmax     = hmax
    if (present(fac1))     me%fac1     = fac1
    if (present(fac2))     me%fac2     = fac2

    if (present(nmax)) then
        if ( nmax<=0 ) then
            if ( me%iprint/=0 ) &
                write (me%iprint,*) ' wrong input nmax=', nmax
            status_ok = .false.
        else
            me%nmax = nmax
        end if
    end if

    if (present(safe)) then
        if ( safe>=1.0_wp .or. safe<=1.0e-4_wp ) then
            if ( me%iprint/=0 ) &
                write (me%iprint,*) ' curious input for safety factor safe:', &
                                    safe
            status_ok = .false.
        else
            me%safe = safe
        end if
    end if

    if (present(beta)) then
        if ( beta<=0.0_wp ) then
           me%beta = 0.0_wp
        else
           if ( beta>0.2_wp ) then
              if ( me%iprint/=0 ) write (me%iprint,*) &
                                    ' curious input for beta: ', beta
              status_ok = .false.
           else
              me%beta = beta
           end if
        end if
    end if

    if (present(icomp)) then
        me%nrdens = size(icomp)
        !check validity of icomp array:
        if (size(icomp)<=me%n .and. all(icomp>0 .and. icomp<=me%n)) then
            allocate(me%icomp(me%nrdens));  me%icomp = icomp
            allocate(me%cont(8*me%nrdens)); me%cont = 0.0_wp
        else
            if ( me%iprint/=0 ) write (me%iprint,*) &
                                  ' invalid icomp array: ',icomp
            status_ok = .false.
        end if
    end if

    end subroutine set_parameters