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!)
cheers,
Rolf Turner
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