style: align nonautonomous naming with solver conventions

Agent-Logs-Url: https://github.com/ivan-pi/stiff3/sessions/67f692d9-43f0-4337-94d3-193b5edcdf71

Co-authored-by: ivan-pi <21085643+ivan-pi@users.noreply.github.com>

Author: Copilot

src/stiff3_solver.f90

@@ -302,6 +302,7 @@ subroutine stiff3_nonautonomous(n,fun,dfun,dfdx,out,nprint,x0,x1,h0,eps,w,y)
 
   contains
 
+    ! Augmented rhs: x' = 1 and y' = f(x,y)
     subroutine fun_aug(naug,yi,fi)
       integer, intent(in) :: naug
       real(wp), intent(in) :: yi(naug)
@@ -310,6 +311,9 @@ subroutine fun_aug(naug,yi,fi)
       call fun(n,yi(1),yi(2:),fi(2:))
     end subroutine
 
+    ! Augmented Jacobian:
+    ! [0      0 ]
+    ! [df/dx df/dy]
     subroutine jac_aug(naug,yi,dfi)
       integer, intent(in) :: naug
       real(wp), intent(in) :: yi(naug)
@@ -319,12 +323,12 @@ subroutine jac_aug(naug,yi,dfi)
       call dfun(n,yi(1),yi(2:),dfi(2:,2:))
     end subroutine
 
-    subroutine out_aug(x,yi,iha,qa)
+    subroutine out_aug(x,yi,ih,qa)
       real(wp), intent(in) :: x
       real(wp), intent(in) :: yi(:)
-      integer, intent(in) :: iha
+      integer, intent(in) :: ih
       real(wp), intent(in) :: qa
-      call out(x,yi(2:),iha,qa)
+      call out(x,yi(2:),ih,qa)
     end subroutine
 
   end subroutine

test/nonautonomous.f90

@@ -24,28 +24,28 @@ program nonautonomous
 
 contains
 
-  subroutine fun(n,t,y,f)
+  subroutine fun(n,x,y,f)
     integer, intent(in) :: n
-    real(wp), intent(in) :: t
+    real(wp), intent(in) :: x
     real(wp), intent(in) :: y(n)
     real(wp), intent(inout) :: f(n)
-    f(1) = -y(1) + sin(t)
+    f(1) = -y(1) + sin(x)
   end subroutine
 
-  subroutine jac(n,t,y,df)
+  subroutine jac(n,x,y,df)
     integer, intent(in) :: n
-    real(wp), intent(in) :: t
+    real(wp), intent(in) :: x
     real(wp), intent(in) :: y(n)
     real(wp), intent(inout) :: df(n,n)
     df(1,1) = -1.0_wp
   end subroutine
 
-  subroutine dfdx(n,t,y,fx)
+  subroutine dfdx(n,x,y,fx)
     integer, intent(in) :: n
-    real(wp), intent(in) :: t
+    real(wp), intent(in) :: x
     real(wp), intent(in) :: y(n)
     real(wp), intent(inout) :: fx(n)
-    fx(1) = cos(t)
+    fx(1) = cos(x)
   end subroutine
 
   subroutine out(t,y,ih,qa)