Environmental problems.

On 14-02-25 3:08 AM, Rolf Turner wrote:

I have a function that makes use of the ode() function from the
"deSolve" package.  I am trying to find a way of getting it to put out a
"progress report" every "t.int" time units (by "progress report" I just
mean reporting what time it's got up to).

I thought to put code something like the following in my "func" function
that gets called by (is an argument to) ode():

cat("Before: time =",tt,"tdone =",tdone,"diff =",tt-tdone,"\n")
if(tt - tdone >= 0.1-sqrt(.Machine$double.eps)) {
     cat("Prog. Rep.: time =",tt,"tdone =",tdone,"diff =",tt-tdone,"\n")
     assign("tdone",tt,envir=parent.env(environment()))
}
cat("After: time =",tt,"tdone =",tdone,"diff =",tt-tdone,"\n")

The object "tdone" gets initialized (to 0) outside of func(), so there
is not a problem with "tdone" not being found the first time that func()
gets called by ode().  (I'm hardwiring "t.int=0.1" in the forgoing just
for test/illustration purposes.)  The "Before" and "After" cat()-s are
there to demonstrate what goes wrong.

What goes wrong is that I get no progress report and tdone remains equal
to 0 until tt reaches 0.1. As desired. I then get a progress report and
tdone gets set equal to the first value of tt which is greater than 0.1.
As desired.

Then I get no further progress reports and tdone gets set equal to tt at
every call to func() --- even though tt - tdone = 0 which is less than
0.1 so the assignment of tdone cannot occur.  And yet it does, keeping
the difference equal to 0.  (*Not* as desired!)

So the function is recognizing that the difference is less than 0.1 in
that it does not execute the cat() statement.  Yet it executes the
assign() statement.  This is clearly impossible! :-)  But it happens.

The output from the cat()-ing, around time = 0.1, looks like:

Before: time = 0.09364548 tdone = 0 diff = 0.09364548
After: time = 0.09364548 tdone = 0 diff = 0.09364548
Before: time = 0.0975779 tdone = 0 diff = 0.0975779
After: time = 0.0975779 tdone = 0 diff = 0.0975779
Before: time = 0.0975779 tdone = 0 diff = 0.0975779
After: time = 0.0975779 tdone = 0 diff = 0.0975779
Before: time = 0.09698997 tdone = 0 diff = 0.09698997
After: time = 0.09698997 tdone = 0 diff = 0.09698997
Before: time = 0.1009224 tdone = 0 diff = 0.1009224
Prog. Rep.: time = 0.1009224 tdone = 0 diff = 0.1009224
After: time = 0.1009224 tdone = 0.1009224 diff = 0
Before: time = 0.1009224 tdone = 0.1009224 diff = 0
After: time = 0.1009224 tdone = 0.1009224 diff = 0
Before: time = 0.1003344 tdone = 0.1003344 diff = 0  <--------------|
After: time = 0.1003344 tdone = 0.1003344 diff = 0
Before: time = 0.1042669 tdone = 0.1042669 diff = 0
After: time = 0.1042669 tdone = 0.1042669 diff = 0

It's at that line indicated by "<----|", 4 lines from the bottom of the
forgoing display, where things go to hell in a handcart.  Why (how on
earth can) tdone change from 0.1009224 to 0.1003344, given that the
difference is 0 whence no assignment of tdone should take place?

What am I not seeing?  Can anyone help me out?  I'm going mad!
***MAD*** I tell you! :-)

Suggestions as to a better way of accomplishing my desired goal of
producing progress reports would also be welcome.

I am not at all sure that assigning "tdone" in parent.env(environment())
is the right thing to do.  I need to assign it in such a way and in such
a location that its value will persist
from call to call of "func".  Words of wisdom about this would be
gratefully received.  (I don't really grok environments.  I just try
things until *something* works!)

You don't show us everything (we want the full Monty!), so it's hard to
say what's going wrong.  My guess would be that you have both a local
copy as well as a parent copy of some variable, and your test is
consulting the wrong one.

A better approach to what you are doing (better since yours modifies
things in the global environment, and that can be dangerous; other code
might modify it too) is the following.  Create your func in a local
block, and it will have it's own mini-environment associated with it.
Put tdone there.  For example,

func <- local({
   # local() creates an environment; that's where tdone will live
   tdone <- 0

   # this function's environment will be the one created by
   # local(), so it will see tdone, but other code won't see it.

   function(x) {
     # the timing stuff
     tt <- Sys.time()
     if (tt - tdone > 0.1) {
       cat("Prog rep...")
       tdone <<- tt
     }
     # now the real stuff
     ...
   })