Merging three functions into one

Question

I'm building a program that converts orbital elements into cartesian coordinates.

I want to create a function that does this, converts orbital elements into cartisian coordinates, but I can't get it to work. This is my first time using fortran so I'm still getting used to it.

program conversion

implicit none
real*8 :: EC, A, IC, OM, W, TA, X, Y, Z
real*8, external :: XCARTISIAN, YCARTISIAN, ZCARTISIAN, r

print *, "Insert Oribtal Elements (EC, A, IC, OM, W, TA): "
read *, EC, A, IC, OM, W, TA, X, Y, Z


X = XCARTISIAN(EC, A, IC, OM, W, TA)
Y = YCARTISIAN(EC, A, IC, OM, W, TA)
Z = ZCARTISIAN(EC, A, IC, OM, W, TA)

print *, "X : ", X, "Y : ", Y, "Z : ", Z

end program conversion



real*8 function XCARTISIAN(EC, A, IC, OM, W, TA)

implicit none
real*8, intent(in) :: EC, A, IC, OM, W, TA
real*8 :: XCARTISIAN, r

r = A(1-EC**2)/(1+EC*COS(TA))
XCARTISIAN = r(COS(OM)*COS(W+TA)-SIN(OM)*SIN(W+TA)*COS(IC))

return

end function XCARTISIAN

real*8 function YCARTISIAN(EC, A, IC, OM, W, TA)

implicit none
real*8, intent(in) :: EC, A, IC, OM, W, TA
real*8 :: YCARTISIAN

r = A(1-EC**2)/(1+EC*COS(TA))
YCARTISIAN = r(SIN(OM)*COS(W+TA)+COS(OM)*SIN(W+TA)*COS(IC))

return

end function YCARTISIAN


real*8 function ZCARTISIAN(EC, A, IC, OM, W, TA)

implicit none
real*8, intent(in) :: EC, A, IC, OM, W, TA
real*8 :: ZCARTISIAN

r = A(1-EC**2)/(1+EC*COS(TA))
ZCARTISIAN = r(SIN(W+F)*SIN(IC)

return

end function ZCARTISIAN

How can I get this to work and make a single function that does this instead of three separate ones for X, Y and Z individually?

The conversion formulas are as follows:

X = r(COS(OM)*COS(W+TA)-SIN(OM)*SIN(W+TA)*COS(IC))
Y = r(SIN(OM)*COS(W+TA)+COS(OM)*SIN(W+TA)*COS(IC))
Z = r(SIN(W+F)*SIN(IC)

where,

r = A(1-EC**2)/(1+EC*COS(TA))

Welcome. Use tag [tag:fortran] for all Fortran questions. You can add a version if you need to distinguish a specific one. — Vladimir F Героям слава, Nov 16 '16 at 11:30
You can't change your question that much! You can't invalidate existing answers. — Vladimir F Героям слава, Nov 17 '16 at 10:01
Sorry, but in past questions people have told me to update the current question as new problems come up. I've been yelled at for not updating the main question and for updating the question... — Frederico Arez, Nov 17 '16 at 10:11
You see? Its hard to please everyone. Anyways, thank you so much! I got the program working already :). Thank you! — Frederico Arez, Nov 17 '16 at 10:19

Holmz · Answer 1 · 2016-11-16T12:54:43.277

Maybe Put your functions into a module?

MODULE ORBITCANDY 
IMPLICIT NONE
PRIVATE

TYPE(Cart_typ)
  REAL*8 X
  REAL*8 Y
  REAL*8 Z
END TYPE Cart_typ
PUBLIC :: Cart_Typ

TYPE(OE_typ)
  REAL*8 EC
  REAL*8 A
  REAL*8 IC
  REAL*8 OM
  REAL*8 W
  REAL*8 TA
END TYPE OE_typ
PUBLIC :: OE_Typ

PUBLIC :: OE2CART

CONTAINS

function OE2Cart(OE)
implicit none
TYPE(OE_Typ) , INTENT(IN   ) :: OE
TYPE(Cart_Typ)               :: OE2Cart
real*8                       :: EC, A, IC, OM, W, TA
real*8                       :: XCARTISIAN, r

EC = OE%EC
A  = OE%A
IC = OE%IC
OM = OE%OM
W  = OE%W
TA = OE%TA
OE2Cart%X = XCARTISIAN(EC, A, IC, OM, W, TA)
OE2Cart%Y = YCARTESIAN(EC, A, IC, OM, W, TA)
OE2Cart%Z = ZCARTESIAN(EC, A, IC, OM, W, TA)

RETURN
END FUNCTION OE2CART

!%%%%%%%%%%%%%%
real*8 function YCARTISIAN(EC, A, IC, OM, W, TA)
implicit none
TYPE(OE_Typ) , INTENT(IN   ) :: OE
real*8, intent(in) :: EC, A, IC, OM, W, TA
real*8 :: XCARTISIAN, r

r = A(1-EC**2)/(1+EC*COS(TA))
XCARTISIAN = r(COS(OM)*COS(W+TA)-SIN(OM)*SIN(W+TA)*COS(IC))

return
end function XCARTISIAN

!%%%%%%%%%%%%%%
real*8 function YCARTISIAN(EC, A, IC, OM, W, TA)
implicit none
real*8, intent(in) :: EC, A, IC, OM, W, TA
real*8 :: YCARTISIAN

r = A(1-EC**2)/(1+EC*COS(TA))
YCARTISIAN = r(SIN(OM)*COS(W+TA)+COS(OM)*SIN(W+TA)*COS(IC))

return
end function YCARTISIAN


   !%%%%%%%%%%%%%%
real*8 function ZCARTISIAN(EC, A, IC, OM, W, TA)

implicit none
real*8, intent(in) :: EC, A, IC, OM, W, TA
real*8 :: ZCARTISIAN

r = A(1-EC**2)/(1+EC*COS(TA))
ZCARTISIAN = r(SIN(W+F)*SIN(IC)

return

end function ZCARTISIAN

END MODULE ORBITCANDY

And one for R, and then CART2GEODETIC, Etc...

program conversion
USE ORBITCANDY
implicit none
TYPE(OE_Typ)   :: OE
TYPE(Cart_Typ) :: Cart
real*8, external :: r ! Add this one above

print *, "Insert Oribtal Elements (EC, A, IC, OM, W, TA): "
read *, OE%EC, OE%A, OE%IC, OE%OM, OE%W, OE%TA

print *, "Insert Oribtal Elements (EC, A, IC, OM, W, TA): "
read *, OE%EC, OE%A, OE%IC, OE%OM, OE%W, OE%TA

XYZ = OE2CART(OE)
print *, "X : ", XYZ%X, "Y : ", XYZ%Y, "Z : ", XYZ%Z

end program conversion

There is no compiler in the iPad, so I am sure to have a typo...

Why does seemingly simple Fortran make my eyes bleed each time again? — rubenvb, Nov 16 '16 at 12:43
Baby steps @rubenvb but the program (main) looks simpler. I could put ISO_C_BINDING in so you could use it with C (?). — Holmz, Nov 16 '16 at 12:45

Vladimir F Героям слава · Accepted Answer · 2016-11-17T10:07:27.340

1

The most straightforward thing to do is to make a single subroutine. Best placed in a module, but that is optional (But IMHO all functions and subroutines should be in some module).

subroutine XYZCARTISIAN(XCARTISIAN, YCARTISIAN, ZCARTISIAN, EC, A, IC, OM, W, TA)

  implicit none
  real*8 :: XCARTISIAN, YCARTISIAN, ZCARTISIAN
  real*8, intent(in) :: EC, A, IC, OM, W, TA
, r

  r = A(1-EC**2)/(1+EC*COS(TA))

  XCARTISIAN = r*(COS(OM)*COS(W+TA)-SIN(OM)*SIN(W+TA)*COS(IC))
  YCARTISIAN = r*(SIN(OM)*COS(W+TA)+COS(OM)*SIN(W+TA)*COS(IC))
  ZCARTISIAN = r*(SIN(W+F)*SIN(IC)
end subroutine

This will also be faster, because you compute r only once and you make just one sub-program call.

Please note:

real*8 is completely non-standard, it is not Fortran.
Use indentation to make your code more readable.
No return is necessary there, us it only to return prematurely.

edited Nov 17 '16 at 10:07

answered Nov 16 '16 at 17:50

Vladimir F Героям слава

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Ok! This is much simpler! – Frederico Arez Nov 17 '16 at 08:27
If I understand correctly, to use a subroutine I need to use the CALL() function. How do I do this in the main part of my code where I want to assign XCARTISIAN to X and so on? – Frederico Arez Nov 17 '16 at 09:17
You just `call XYZCARTISAN(X, Y, Z, EC, ...)` – Vladimir F Героям слава Nov 17 '16 at 09:28
Oh! Ok! I think I understand. Also, gfortran says that the XCARTISIAN, YCARTISIAN and ZCARTISIAN statements within the subroutine are unclassiable. What does this mean? – Frederico Arez Nov 17 '16 at 09:53
I just copied the code from your question. You need to use `*` for multiplication. – Vladimir F Героям слава Nov 17 '16 at 10:05

Merging three functions into one

2 Answers2