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Rewrite of the deco code

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o) Instead of using gradient factors as means of comparison, I now use
   pressure (as in: maximal ambient pressure).

o) tissue_tolerance_calc() now computes the maximal ambient pressure now
   respecting gradient factors. For this, it needs to know about the
   surface pressure (as refernce for GF_high), thus gets *dive as an
   argument. It is called from add_segment() which this also needs *dive
   as an additional argument.

o) This implies deco_allowed_depth is now mainly a ambient-pressure to
   depth conversion with decorations to avoid negative depth (i.e. no deco
   obliation), implementation of quantization (!smooth => multiples of 3m)
   and explicit setting of last deco depth (e.g. 6m for O2 deco).

o) gf_low_pressure_this_dive (slight change of name), the max depth in
   pressure units is updated in add_segment. I set the minimal value in
   buehlmann_config to the equivalent of 20m as otherwise good values of
   GF_low add a lot of deco to shallow dives which do not need deep stops
   in the first place.

o) The bogus loop is gone as well as actual_gradient_limit() and
   gradient_factor_calculation() and large parts of deco_allowed_depth()
   although I did not delete the code but put it in comments.

o) The meat is in the formula in lines 147-154 of deco.c. Here is the
   rationale:

   Without gradient factors, the M-value (i.e the maximal tissue pressure)
   at a given depth is given by ambient_pressure / buehlmann_b + a.

   According to "Clearing Up The Confusion About "Deep Stops" by Erik C.
   Baker (as found via google) the effect of the gradient factors is no
   replace this by a reduced affine relation (i.e. another line) such that
   at the surface the difference between M-value and ambient pressure is
   reduced by a factor GF_high and at the maximal depth by a factor
   GF_low.

   That is, we are looking for parameters alpha and beta such that

   alpha surface + beta = surface + gf_high * (surface/b + a - surface)

   and

   alpha max_p + beta = max_p + gf_low * (max_p/b + a - max_p)

   This can be solved for alpha and beta and then inverted to obtain the
   max ambient pressure given tissue loadings. The result is the above
   mentioned formula.

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
This commit is contained in:
Robert C. Helling 2013-01-08 15:37:41 +01:00 • committed by Dirk Hohndel
parent e3bdbb7c0f
commit 67d59ff018
5 changed files with 109 additions and 78 deletions
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4
divelist.c
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@ -837,7 +837,7 @@ static void add_dive_to_deco(struct dive *dive)
int depth = 0.5 + psample->depth.mm + (j - t0) *
(sample->depth.mm - psample->depth.mm) / (t1 - t0);
(void) add_segment(depth_to_mbar(depth, dive) / 1000.0,
&dive->cylinder[sample->sensor].gasmix, 1, sample->po2 / 1000.0);
&dive->cylinder[sample->sensor].gasmix, 1, sample->po2 / 1000.0, dive);
}
}
}
@ -882,7 +882,7 @@ double init_decompression(struct dive *dive)
printf("added dive #%d\n", pdive->number);
dump_tissues();
#endif
tissue_tolerance = add_segment(surface_pressure, &air, surface_time, 0.0);
tissue_tolerance = add_segment(surface_pressure, &air, surface_time, 0.0, dive);
#if DECO_CALC_DEBUG & 2
printf("after surface intervall of %d:%02u\n", FRACTION(surface_time,60));
dump_tissues();