Offtopic really for it's not a a fortran language question, but I'm
sure many in here have dealt with the problem at some point in time.

Robert Singer ____.com> wrote:

Sure it does. And that part is even a Fortran-specific question, so you
ger "credit" for being on topic after all. :-)

See such things as anint. You have to scale as needed to get the
appropriate rounding, but that's trivially doable. How to do things like
rounding has come up here more than once, with several answers. Anint is
one (or just plain aint, as you are probably talking about rounding
down, also known as truncation, or rounding up, instead of rounding to
nearest). Doing internal writes is another way.

For example, 5.*aint(x/5) should round down to a multiple of 5.

The rounding part is simple, per above.

Robert Singer wrote:

(snip)

X and Y are separate, so just consider one. This is based on
one I have used and modified over the years:

You need Xmin, Xmax, and the desired axis length: Axlen
(number of intermediate tick marks.) Compute the value
for the low end (TL) and tick increment (TX).

real table(14)
! available scale factors, with power of 10 removed
! up to 20 allows for some roundoff that might occur
! on 10th inch graph paper, you might want /1, 2, 5, 10, 20/
data table/1.,1.2,1...

Robert Singer wrote:

...

...

Richard has given the gist; like most I've also had routines that did
such but haven't had to use them in ages. My recollection is that mine
did basically what Richard describes but used predefined factors of
1,2,4,5,10 as the ranges and basically turned into a CASE statement block.

--

My approach is pretty much as others have described:

1. Get min and max based on data
2. Try a step size.
For integer data I try 1,2,5,10,20,50,... Round min down to next lower
multiple of step size.
Round max up to next higher multiple of step size.
3. Determine number of tick mark labels that the step size would require. If
too many (>10), back to step 2
to try the next step size.

One other thing to consider.

Do you want to have a default range? We often plot water releases from
dams. We make the default range
of data go from 0 to turbine discharge capaciity, but will increase the
range if there is plot data outside the default
(when the dam is spilling water). Having a default range makes it easier to
compare graphs.

"glen herrmannsfeldt" ugcs.caltech.edu> wrote in message
news:nZGdnQcWOaOeAU3VnZ2dnUVZ_qrinZ2d@comcast.com...

In addition to suggestions received so far, I will note that
if one uses log base 10 (i.e., common logs) it is possible
to find the next higher power of ten that contains the
values in question. This is useful for a starting range
when scaling may be wildly disparate form one set to the next.
It is also useful for gridding and generating tick marks.

Example (F77 from early 1980s, target processor M680000):

*----------
ENTRY GENTIX
TIKS = .TRUE.
GRDS = .FALSE.
XOR = .TRUE.
6789 CONTINUE
XRANGE = XMAX - XMIN
YRANGE = YMAX - YMIN
XPOW = ALOG10(XRANGE)
YPOW =...

On Sep 17, 11:42 am, "Kevin G. Rhoads" alum.mit.edu> wrote:

GaryScott wrote:

...[old sample code elided]...

Yeah, I just quit worrying about plotting inside the Fortran
cod

On Wed, 17 Sep 2008 17:45:54 -0500, dpb non.net> wrote:

I've used tecplot in the past, version 8 (I think; was a long time
ago). Very nice and friendly piece of software, unfortunately a little
on the expensive side (maybe things changed now, although I somehow
doubt it).

But I do not see how tecplot even compares to plotting inside fortran.
Aside the tecplot sdk which I see on their web, I cannot get tecplto
plots inside my program to act interactivly. Tecplot is post-plotting.

On Wed, 17 Sep 2008 00:56:49 -0500, dpb non.net> wrote:

Yes, I agree. What I was missing, and what Richard first mentioned,
was the log10 part. I was having trouble figuring how to round it up
to a "nice" value, and just didn't think of changing the axis system
(interesting how fortran programmers have a pragmatic view on these
problems).