[ADOL-C] piecewise defined functions

[Philipp Bender]

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Dear list,

as always when learning a new tool ... as soon as one issue seems
solved, the next one shows up, so this is my second question today ...

I have a function which can be considered as piecewise. It's a
polygonal line strip, and the function returns the shortest distance
to one of the strips, but with some interpolation tricks to circumvent
discontinuities and so on. So contrary to "usual" piecewise
definitions, I cannot simply look at the parameters to see which
definition I have to use at this particular point.

Basically, I do this (Pseudocode):

fun(x, y):
  dist = big number
  iterate over all segments of the line strip:
    dist'  = segment.distance(x, y)
    dist = min(dist, dist')

  return dist

and somewhere else:

trace_on(0)
fun(...)
trace_off()

Now, I think I cannot simply declare this to be a template and stop
thinking. I assume that now *every* segment's operation stack gets
recorded in the tape, and I end up with something wrong.

My idea was to first have a dry run with doubles (not adoubles), just
to obtain the correct index. Then, with adoubles x and y, call
segment[index].distance(x, y). So with N segments, I need N+1 calls
(instead of N). Not that this would be a problem, I mention it only to
explain what I mean.

Is there an error in my thinking, do I miss something here?

Best regards,
Philipp

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