This routine checks for the presence of a root in the vicinity of the current T, in a manner depending on the input flag JOB. It calls Subroutine DROOTS to locate the root as precisely as possible.
In addition to variables described previously, DRCHEK uses the following for communication:
integer flag indicating type of call:
| JOB | Description |
|---|---|
| 1 | means the problem is being initialized, and DRCHEK |
| is to look for a root at or very near the initial T. | |
| ! | |
| 2 | means a continuation call to the solver was just |
| made, and DRCHEK is to check for a root in the | |
| relevant part of the step dlsr taken. | |
| ! | |
| 3 | means a successful step was just taken, and DRCHEK |
| is to look for a root in the interval of the step. |
array of length NG, containing the value of g at T = T0. G0 is input for JOB .ge. 2, and output in all cases.
arrays of length NG for work space.
completion flag:
| IRT | Description |
|---|---|
| 0 | means no root was found. |
| -1 | means JOB = 1 and a root was found too near to T. |
| 1 | means a legitimate root was found (JOB = 2 or 3). |
On return, T0 is the root location, and Y is the corresponding solution vector.
value of T at one endpoint of interval of interest. Only roots beyond T0 in the direction of integration are sought.
T0 is input if JOB .ge. 2, and output in all cases.
T0 is updated by DRCHEK, whether a root is found or not.
dlsr value of T returned by the solver (input only).
copy of TOUT (input only).
input flag showing whether the dlsr step taken had a root. IRFND = 1 if it did, = 0 if not.
copy of ITASK (input only).
copy of NG (input only).
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| integer, | intent(in) | :: | Job | |||
| real | :: | g_sub | ||||
| integer | :: | Neq(*) | ||||
| real(kind=dp) | :: | Y(*) | ||||
| real(kind=dp) | :: | Yh(Nyh,*) | ||||
| integer, | intent(in) | :: | Nyh | |||
| real(kind=dp) | :: | G0(*) | ||||
| real(kind=dp) | :: | G1(*) | ||||
| real(kind=dp) | :: | Gx(*) | ||||
| integer | :: | Jroot(*) | ||||
| integer, | intent(out) | :: | Irt |
| Type | Visibility | Attributes | Name | Initial | |||
|---|---|---|---|---|---|---|---|
| real(kind=dp), | public | :: | hming | ||||
| integer, | public | :: | i | ||||
| integer, | public | :: | iflag | ||||
| integer, | public | :: | jflag | ||||
| real(kind=dp), | public | :: | t1 | ||||
| real(kind=dp), | public | :: | temp1 | ||||
| real(kind=dp), | public | :: | temp2 | ||||
| real(kind=dp), | public | :: | x | ||||
| logical, | public | :: | zroot |
subroutine drchek(Job,g_sub,Neq,Y,Yh,Nyh,G0,G1,Gx,Jroot,Irt) ! integer, intent(in) :: Job external g_sub integer :: Neq(*) real(kind=dp) :: Y(*) integer,intent(in) :: Nyh real(kind=dp) :: Yh(Nyh,*) real(kind=dp) :: G0(*) real(kind=dp) :: G1(*) real(kind=dp) :: Gx(*) integer :: Jroot(*) integer,intent(out) :: Irt real(kind=dp) :: hming, t1, temp1, temp2, x integer :: i, iflag, jflag logical :: zroot Irt = 0 do i = 1, dlsr%ngc Jroot(i) = 0 enddo hming = (abs(dls1%tn)+abs(dls1%h))*dls1%uround*100.0D0 select case (Job) case (2) if ( dlsr%irfnd/=0 ) then ! If a root was found on the previous step, evaluate G0 = g(T0). ------- call dintdy(dlsr%t0,0,Yh,Nyh,Y,iflag) call g_sub(Neq,dlsr%t0,Y,dlsr%ngc,G0) dlsr%nge = dlsr%nge + 1 zroot = .false. do i = 1, dlsr%ngc if ( abs(G0(i))<=0.0D0 ) zroot = .true. enddo if ( zroot ) then ! g has a zero at T0. Look at g at T + (small increment). ------------- temp1 = sign(hming,dls1%h) dlsr%t0 = dlsr%t0 + temp1 if ( (dlsr%t0-dls1%tn)*dls1%h<0.0D0 ) then call dintdy(dlsr%t0,0,Yh,Nyh,Y,iflag) else temp2 = temp1/dls1%h do i = 1, dls1%n Y(i) = Y(i) + temp2*Yh(i,2) enddo endif call g_sub(Neq,dlsr%t0,Y,dlsr%ngc,G0) dlsr%nge = dlsr%nge + 1 zroot = .false. do i = 1, dlsr%ngc if ( abs(G0(i))<=0.0D0 ) then Jroot(i) = 1 zroot = .true. endif enddo if ( zroot ) then ! g has a zero at T0 and also close to T0. Return root. --------------- Irt = 1 return endif endif endif ! G0 has no zero components. Proceed to check relevant interval. ------ if ( dls1%tn==dlsr%tlast ) then return endif case (3) case default ! ! Evaluate g at initial T, and check for zero values. ------------------ dlsr%t0 = dls1%tn call g_sub(Neq,dlsr%t0,Y,dlsr%ngc,G0) dlsr%nge = 1 zroot = .false. do i = 1, dlsr%ngc if ( abs(G0(i))<=0.0D0 ) zroot = .true. enddo if ( zroot ) then ! g has a zero at T. Look at g at T + (small increment). -------------- temp2 = max(hming/abs(dls1%h),0.1D0) temp1 = temp2*dls1%h dlsr%t0 = dlsr%t0 + temp1 do i = 1, dls1%n Y(i) = Y(i) + temp2*Yh(i,2) enddo call g_sub(Neq,dlsr%t0,Y,dlsr%ngc,G0) dlsr%nge = dlsr%nge + 1 zroot = .false. do i = 1, dlsr%ngc if ( abs(G0(i))<=0.0D0 ) zroot = .true. enddo if ( zroot ) then ! g has a zero at T and also close to T. Take error return. ----------- Irt = -1 return endif endif return endselect ! ! Set T1 to TN or TOUTC, whichever comes first, and get g at T1. ------- if ( dlsr%itaskc/=2 .and. dlsr%itaskc/=3 .and. dlsr%itaskc/=5 ) then if ( (dlsr%toutc-dls1%tn)*dls1%h<0.0D0 ) then t1 = dlsr%toutc if ( (t1-dlsr%t0)*dls1%h<=0.0D0 ) then return endif call dintdy(t1,0,Yh,Nyh,Y,iflag) endif t1 = dls1%tn do i = 1, dls1%n Y(i) = Yh(i,1) enddo endif call g_sub(Neq,t1,Y,dlsr%ngc,G1) dlsr%nge = dlsr%nge + 1 ! Call DROOTS to search for root in interval from T0 to T1. ------------ jflag = 0 do call droots(dlsr%ngc,hming,jflag,dlsr%t0,t1,G0,G1,Gx,x,Jroot) if ( jflag>1 ) then dlsr%t0 = x !X!call dcopy(dlsr%ngc,Gx,1,G0,1) G0(1:dlsr%ngc) = Gx(1:dlsr%ngc)!X! if ( jflag/=4 ) exit return else call dintdy(x,0,Yh,Nyh,Y,iflag) call g_sub(Neq,x,Y,dlsr%ngc,Gx) dlsr%nge = dlsr%nge + 1 endif enddo ! Found a root. Interpolate to X and return. -------------------------- call dintdy(x,0,Yh,Nyh,Y,iflag) Irt = 1 end subroutine drchek