On Fri, 12 Jan 2007, Huazhong Wang wrote:
i want to take out the Ex at point (0 0 0) after running. my code is below:
...
(define (myfun Ex) (get-field-point Ex (vector3 0 0 0)))
...
(run-util 100
(at-end (output-field-function "Ex" (list Ex) myfun))
)
...
but meep stops running, its response is: Error: wrong number of arguments to
#<procedure myfun(Ex)>
i am confued here. who can tell me why?
You have many, many errors in this code, I'm afraid. I hardly know where
to begin.
First, as explained in the manual, the function (myfun) you pass to
output-field-function must take as its first argument the position vector
r. The subsequent arguments are then the field components that you
requested (here, Ex). So, for example, a valid function would be say:
(define (myfun r ex) ex)
which just returns the value of ex, ignoring the position argument.
Second, your function myfun is called at every point in the volume and is
*passed* the value of the field. There is no need to call
get-field-point, and in fact calling get-field-point inside your field
function will deadlock on a parallel machine.
Third, in your "myfun" function you took a parameter named "Ex". Even if
this were correct, which it isn't as I explained above, it would mean that
"Ex" inside that function would be the *value* of the Ex field at each
point. Then, even if calling get-field-point were correct (which it isn't
as I explained above), you would be passing the *value* of the Ex field as
the first argument, and not the symbolic name "Ex" for the component,
causing get-field-point to fail.
Fourth, by passing (output-field-function ...) to run-until, you are
passing the *result* of *calling* the function, and not the function
itself. This means that you are actually calling output-field-function
*before* starting your run-until. What you want to do is to pass a
*function* to run-until, which *calls* output-field-function, so that this
function can be called on each time step, or in this case at the end of
the simultation. See also my previous message to the mailing list where I
explained this point.
Fifth, if you only want to output the field at a *single* point (0,0,0),
then you need to do one of two things. (By default,
output-field-function, like all the output functions, outputs the value of
calling your function for every point in the computational cell.) You
can either:
1) use (in-volume (volume (size 0 0 0) (center 0 0 0)) ......)
as another poster suggested. This will output an HDF5
file with a dataset consisting of a single point.
(if you are outputting this data at lots of time-steps, not
just at the end, you might also want to use to-appended
to create a single HDF5 file with a 1d dataset with
that point as a function of time, rather than a whole
bunch of individual single-point HDF5 files)
or
2) don't use HDF5 files at all, which are overkill for outputting
a single point. Just use the "print" function to output
directl to standard output. For example:
(define (myoutput)
(print "myoutput:, " (meep-time) ", "
(get-field-point Ex (vector3 0 0 0)) "\n"))
And then do
(run-until 200 my-output)
or whatever you want. Note that in this case you *do*
just want to call get-field-output directly.
Steven
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