Is it allowed to have one do loop completely within another
do loop in Fortran?

On 3/27/2011 8:34 PM, Anne Onime wrote:
> Is it allowed to have one do loop completely within another
> do loop in Fortran?

Of course...know of no programming language that prohibits such a 
construct.  Why the question re: Fortran?

--

dpb <none@non.net> wrote:

> On 3/27/2011 8:34 PM, Anne Onime wrote:
> > Is it allowed to have one do loop completely within another
> > do loop in Fortran?
> 
> Of course...know of no programming language that prohibits such a 
> construct.  Why the question re: Fortran?

It is not only allowed, it is very, very common. There probably exist
non-trivial programs that don't have such a thing, but they are likely
rare. As dpb notes, that applies to most languages.

-- 
Richard Maine                    | Good judgment comes from experience;
email: last name at domain . net | experience comes from bad judgment.
domain: summertriangle           |  -- Mark Twain

Anne Onime <anonymous@rip.ax.lt> wrote:

> Is it allowed to have one do loop completely within another
> do loop in Fortran?

It definitely does not allow one do loop partially
within another.  Completely within goes back to Fortran I,
allong with extended-range-of-the-DO.  (I believe the latter
has now been removed, though.)

-- glen

On 3/28/2011 2:34 PM, Anne Onime wrote:
> Is it allowed to have one do loop completely within another
> do loop in Fortran?
>

I think the deepest nesting I ever did was about 6.

On Mar 28, 8:33=A0am, Gib Bogle <g.bo...@auckland.ac.nz> wrote:
> On 3/28/2011 2:34 PM, Anne Onime wrote:
>
> > Is it allowed to have one do loop completely within another
> > do loop in Fortran?
>
> I think the deepest nesting I ever did was about 6.

My sudoku programs go to a depth of 8 (=3D 9 - 1).

Regards,

Mike Metcalf

m_b_metcalf <michaelmetcalf@compuserve.com> wrote:

> On Mar 28, 8:33 am, Gib Bogle <g.bo...@auckland.ac.nz> wrote:
> > On 3/28/2011 2:34 PM, Anne Onime wrote:
> >
> > > Is it allowed to have one do loop completely within another
> > > do loop in Fortran?
> >
> > I think the deepest nesting I ever did was about 6.
> 
> My sudoku programs go to a depth of 8 (= 9 - 1).

I think I once ran into a compiler with a limit of 7 or so, which I once
hit. But it was a long time ago, and the memory is vague.

-- 
Richard Maine                    | Good judgment comes from experience;
email: last name at domain . net | experience comes from bad judgment.
domain: summertriangle           |  -- Mark Twain

On 3/27/2011 8:34 PM, Anne Onime wrote:
> Is it allowed to have one do loop completely within another
> do loop in Fortran?
>
Try solving Dudeney puzzle of 1924 by writing a Fortran program:

Find single-decimal-digit values of the letters in the following addition:

        S E N D
    +   M O R E
      ---------
    = M O N E Y

If you take a simple enumerative approach, you will use an 8-deep nested 
loop.

-- mecej4

Richard Maine <nospam@see.signature> wrote:

(snip on DO nesting depth)

> I think I once ran into a compiler with a limit of 7 or so, which I once
> hit. But it was a long time ago, and the memory is vague.

I believe I have known optimizing compilers that would stop
optimizing deeply nested loops, but I don't remember one that
disallowed them.

-- glen

On 3/28/11 1:33 AM, Gib Bogle wrote:
> On 3/28/2011 2:34 PM, Anne Onime wrote:
>> Is it allowed to have one do loop completely within another
>> do loop in Fortran?
>>
>
> I think the deepest nesting I ever did was about 6.

I once saw a nesting that went 15 deep!  It was in a bug report where 
the user was complaining about the spelling in the error message.  We 
changed the spelling and he was happy, or at least stopped complaining.

Dick Hendrickson

Op 28-03-11 03:34, Anne Onime schreef:
> Is it allowed to have one do loop completely within another
> do loop in Fortran?
>
Hi Anne,


Yes, that is how I solve Laplace equation using Gauss-Seidel iterations.

With 2 level do loops for a 2D equation.

Check out: http://fortran.kootsttra.org.uk/sources/laplace and 
http://fortran.kootstra.org.uk/docs/laplace

Compilation and linking works for Intel Fortran on Linux. Other 
compilers I did not test.


Kind regards,


Jan Gerrit

On Mar 27, 9:34=A0pm, Anne Onime <anonym...@rip.ax.lt> wrote:
> Is it allowed to have one do loop completely within another
> do loop in Fortran?

One common application of nested DO loops is the representation of
matrices. I have an example here:
<http://groups.google.com/group/comp.lang.fortran/msg/
26e5af6a7af410c7>

Google for "fortran matrices DO loops". Here are some more examples:
<http://jblevins.org/log/array-write>
<http://orion.math.iastate.edu/burkardt/papers/
fortran_arrays.html#Loop_Unrolling>

agt
--
Freedom - no pane, all gaiGN!

Code Art Now
http://codeartnow.com
Email: a...@codeartnow.com

"Richard Maine" <nospam@see.signature> wrote in message 
news:1jytdqj.1v519whc00n8qN%nospam@see.signature...
> m_b_metcalf <michaelmetcalf@compuserve.com> wrote:
>
>> On Mar 28, 8:33 am, Gib Bogle <g.bo...@auckland.ac.nz> wrote:
>> > On 3/28/2011 2:34 PM, Anne Onime wrote:
>> >
>> > > Is it allowed to have one do loop completely within another
>> > > do loop in Fortran?
>> >
>> > I think the deepest nesting I ever did was about 6.
>>
>> My sudoku programs go to a depth of 8 (= 9 - 1).
>
> I think I once ran into a compiler with a limit of 7 or so, which I once
> hit. But it was a long time ago, and the memory is vague.
>

In a previous employment, some of my erstwhile colleagues wrestled for some 
months with (what appeared to be) an intermittent bug in the Fortran 
compiler, that manifested as the compiler error "Do-loops are nested more 
than 64 deep". Turned out to be a hardware problem.


-- 
Qolin

Email: my qname at domain dot com
Domain: qomputing 

mecej4 <mecej4_nospam@operamail.com> wrote:
> Try solving Dudeney puzzle of 1924 by writing a Fortran program:
 
> Find single-decimal-digit values of the letters in the following addition:
 
>        S E N D
>    +   M O R E
>      ---------
>    = M O N E Y

Runs in 0.08s on this computer.
It could be faster by changing the loop order, such that
some of the IF statements could be moved up.  

      integer s,e,n,d,m,o,r,y
      do 1 s=0,9
      do 1 e=0,9
      if(s.eq.e) goto 1
      do 2 n=0,9
      if(s.eq.n.or.e.eq.n) goto 2
      do 3 d=0,9
      if(d.eq.s.or.d.eq.e.or.d.eq.n) goto 3
      do 4 m=0,9
      if(m.eq.s.or.m.eq.e.or.m.eq.n.or.m.eq.d) goto 4
      do 5 o=0,9
      if(o.eq.s.or.o.eq.e.or.o.eq.n.or.o.eq.d.or.o.eq.m) goto 5
      do 6 r=0,9
      if(r.eq.s.or.r.eq.e.or.r.eq.n) goto 6
      if(r.eq.d.or.r.eq.m.or.r.eq.o) goto 6
      do 7 y=0,9
      if(y.eq.s.or.y.eq.e.or.y.eq.n) goto 7
      if(y.eq.d.or.y.eq.m.or.y.eq.o) goto 7
      if(y.eq.r) goto 7
      if(mod(d+e,10).ne.y) goto 7
      if(mod(n+r+(d+e)/10,10).ne.e) goto 7
      if(mod(e+o+(n+r+(d+e)/10)/10,10).ne.n) goto 7
      if(mod(s+m+(e+o+(n+r+(d+e)/10)/10)/10,10).ne.o) goto 7
      if((s+m+(e+o+(n+r+(d+e)/10)/10)/10)/10.ne.m) goto 7
      if(m.eq.0) goto 7
      print *,  s,e,n,d
      print *,  m,o,r,e
      print *,m,o,n,e,y
7     continue
6     continue
5     continue
4     continue
3     continue
2     continue
1     continue
      stop
      end


-- glen