Fortran complex numbers and do loops

[freja]

I have a very simple question, but have been unable to find an answer for it. When using fortran 90 can you use a DO loop to calculate a complex number? For example:

COMPLEX FUNCTION forwards (tincdum,tstartdum,tenddum,fdum,ydum,idum,wdum&
                                      &,lamdadum)
  IMPLICIT NONE

  REAL, INTENT(IN):: tincdum,tstartdum,tenddum,wdum,lamdadum,ydum,idum
  COMPLEX, INTENT(IN):: ydum,idum
  COMPLEX:: fn

  DO ydum = tstartdum,tenddum,tincdum
   fn = fofy(idum,wdum,lamdadum,ydum,fn)
   ydum = ydum + tincdum*fn
  END DO

  forwards = ydum
 END FUNCTION forwards
[code/]

Thank you

 

[mathmate]

You can use a do loop to calculate a complex number. I am not sure if you can use a complex number for a do loop.

DO ydum = tstartdum,tenddum,tincdum
fn = fofy(idum,wdum,lamdadum,ydum,fn)
ydum = ydum + tincdum*fn
END DO

In the above example, I doubt if ydum can be used as a do loop parameter, nor would it be desirable (under traditional fortran rules) to modify the parameter inside the loop.
On the other hand, it is perfectly legitimate to do what you want to do using a while-loop.
See
http://www.tat.physik.uni-tuebingen.de/~kley/lehre/ftn77/tutorial/loops.html

As a side note, ydum appears in both REAL and COMPLEX declarations. I am not sure if this was intended.

 

[quicknote]

for your question. Yes, you can use a DO loop to calculate a complex number in Fortran 90. In the code provided, the DO loop iterates over the variable ydum, which is declared as a COMPLEX type. This means that ydum can hold both real and imaginary values, allowing for the calculation of a complex number. The function forwards also returns a COMPLEX type, indicating that the calculated value will also be a complex number. Therefore, the DO loop in this code is a valid way to calculate a complex number in Fortran 90.