Keyword arguments.

[sb2601]

I am writinga two stage Runge Kutta code, at present my code calls two subroutines, these are identical except that the the Runge Kutta coefficients are 0.50 and 1.0 for steps 1 and 2 respectively.

To shorten my code I'd like to be able to call the same basic Runge Kutta subroutine twice from my main program,using a RK coefficient of 0.5 for the first call and 1.0 for the second call.

I believe that I may be able to do thisusing keyword arguments when I call my subroutines, but so far haven't got this to work. I'd be grateful if anyone can offer advice or refer me to example coding showing this.

Thank you,

Simon.

[Jugoslav_Dujic]

You don't need keyword arguments -- you just have to pass your calculating function as an EXTERNAL, and pass the parameter as an additional argument, like:

PROGRAM Foo
EXTERNAL Value
...
CALL RungeKutta(Value, 0.5, ...)
CALL RungeKutta(Value, 1.0, ...)
...
SUBROUTINE RungeKutta(Eval, Param, ...)
EXTERNAL:: Eval
REAL:: Param
...
DO i=0,whatever
   x = i * step
   CALL Eval(x, Param, y)
   
END DO
...
END SUBROUTINE RungeKutta

SUBROUTINE Value(x, Param, y)
REAL, INTENT(IN):: x, Param
REAL, INTENT(OUT):: y

y = x**2 + exp(x/Param) - whatever
END SUBROUTINE Value

Instead of EXTERNAL, you could use INTERFACE statements (which is required at least in RungeKutta routine) which would provide more thorough argument-checking than EXTERNAL, but that's the principle.

Jugoslav