Subroutine Euler_Method_Stiff

MODULE Euler_Metodo
USE DATOS, ONLY:t_min,t_max,phi_1,phi_2,phi_3,phi_4,neq,dim
USE FUNCTIONS
USE CHECK_K
PRIVATE

PUBLIC::Euler_exp

contains
SUBROUTINE Euler_exp(Vn,Inc)

        REAL(8),DIMENSION(:,:),POINTER,INTENT(IN) :: Vn
        REAL(8),DIMENSION(dim,neq)::Vn2
        REAL(8)Inc
        REAL(8),DIMENSION(neq)::f
        REAL(8),DIMENSION(neq)::f2
        REAL(8) t_i,t_2
        INTEGER i,j, iter,q
        CHARACTER(8):: Est

        vn(1,1)=phi_1
        vn(1,2)=phi_2
        vn(1,3)=phi_3
        vn(1,4)=phi_4

        vn2(1,1)=phi_1
        vn2(1,2)=phi_2
        vn2(1,3)=phi_3
        vn2(1,4)=phi_4

        q=1
        i=1
        t_i=t_min
        t_2=t_min

    OPEN(10,FILE="write_outs")

    DO WHILE (t_i .le. t_max)

    Iter = i

    print*, "Iter",iter,"i",i
    PRINT*, "t_i",t_i,"inc",inc



    CALL Fun(Vn(i,:),t_i, f) !Asignacion temporal de valores a vn

    Vn(i+1,:)= Vn(i,:) + Inc * f

    t_i = t_i + Inc

    i = i + 1

    DO J=1,2,1

        CALL Fun(Vn2(q,:),t_2,f2) !Asignacion temporal de valores a vn2

        Vn2(q+1,:)= Vn2(q,:) + (Inc/2.d0) * f2

        t2= t2 + Inc/2.d0

        q = q + 1

    END DO

    CALL Check(Vn(i,:),Vn2(q,:), Est)

    CALL Control(Est, t_i, Inc, i, q)


    !IF (i /= Iter) THEN !Se acepto la aproximacion

    Write(10,*) t_i,Vn(i,1),Vn(i,2),Vn(i,3),Vn(i,4)

    !END IF

    END DO
END SUBROUTINE Euler_exp

END MODULE Euler_Metodo