Creating an ODE function Fortran

Question

So I am trying to create a function in Fortran for an ODE and later want to use this code for methods such as Runge-Kutta etc. However I am having trouble coding the initial ode function that I want to use to calculate the rhs given a x and y value.

Here's my code, if anyone can spot anything obvious:

  PROGRAM odemod

  IMPLICIT NONE

  REAL :: x,y,z

  PRINT*,"Enter number one"      
  READ*,x

  PRINT*,"Enter number two"     
  READ*,y

  z=ode(x,y)

  PRINT '("Answer = ",f10.4)',z

CONTAINS

  FUNCTION ode(x,y)      
    IMPLICIT NONE

    REAL, INTENT(IN) :: x,y

    ode=-y+2*x+4           
  END FUNCTION ode

END PROGRAM odemod

and I am getting these errors

f90 -o odemod odemod.f90 odemod.f90:18.2:

  FUNCTION ode(x,y)   1 Error: Function result 'ode' at (1) has no IMPLICIT type odemod.f90:8.9:

  READ*,x
         1 Error: Symbol 'x' at (1) has no IMPLICIT type odemod.f90:10.9:

  READ*,y
         1 Error: Symbol 'y' at (1) has no IMPLICIT type

Well, you just didn't declare your variables. It seems *very obvious* to me. — Vladimir F Героям слава, Nov 21 '17 at 13:32
It is usually good to first search for the error message on the web. It reveals enough resources even from this very site. — Vladimir F Героям слава, Nov 21 '17 at 13:36
The duplicate link https://stackoverflow.com/questions/43768605/function-result-has-no-implicit-type points to the slightly more difficult issue of the undeclared function result. I hope the fact that `x` and `y` are also undeclared will be obvious enough without searching for another duplicate. — Vladimir F Героям слава, Nov 21 '17 at 13:40
ah! I forgot to change it back to x,y at the top instead of a,b. Sorry, I've been messing around with it a lot. But I still get errors — SFL, Nov 21 '17 at 13:46
You must also declare `ode` not just `x` and `y`. See the linked question and answer. The link is there for you to study. — Vladimir F Героям слава, Nov 21 '17 at 13:52

Creating an ODE function Fortran

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