Buhlmann questions

[KenGordon]

Still ugly but here's the first graph with the ceiling.

https://github.com/BlueTrin/diving_decompression/blob/master/buhlmann.ipynb

I get a 404 there.

I think you need to make your repo public or invite me.

 

[BlueTrin]

I get a 404 there.

I think you need to make your repo public or invite me.

Just made it public, sorry !

EDIT: but the Jupyter notebook seems to not work now when I am not logged in ...

 

[BlueTrin]

The link below works ... the Github renderer is broken ...

Jupyter Notebook Viewer

 

[BlueTrin]

In this paper, Eric Baker interpolates GFHi and GFLo, but he seems to use the current stop to fix the GF for the next stop.

That means that GFHi is computed for 6m for example if your last stop is on 6m.
Is that correct ?

Here is an interactive version of my first implementation, you can click on the cells, then press CTRL+ENTER after editing the values to recompute the graph.

GitHub: BlueTrin/diving_decompression/master

disclaimer: don’t use this for any other purpose than testing, playing with it

 

[loosenit2]

The Buhlmann algorithm defines 16 theoretical compartments.

perhaps would be more accurate to say up to 16 theoretical tissue compartments, there are 12 and 8 compartment Buhlmann models as well, although the increase in computing power over the years has made those less necessary.

 

[KenGordon]

In this paper, Eric Baker interpolates GFHi and GFLo, but he seems to use the current stop to fix the GF for the next stop.

That means that GFHi is computed for 6m for example if your last stop is on 6m.
Is that correct ?

Here is an interactive version of my first implementation, you can click on the cells, then press CTRL+ENTER after editing the values to recompute the graph.

GitHub: BlueTrin/diving_decompression/master

disclaimer: don’t use this for any other purpose than testing, playing with it

I literally have to re-read my own code to answer that. I think that GF hi applies at the surface and am certain that GF low applies at the first stop. How you decide that ascending is ok is sort of implementation dependant. You can choose to ascend when the ceiling is shallower than current depth OR ascend when the ceiling hits the next stop depth. The former is a dive computer centric plan, the later a planner centric plan.

Be careful, by the time you are done you will join the group of people that think GF is a horrid hack. This seems much more common amount those that code it up than those that claim it is some kind of open source standard.

 

[KenGordon]

Look at double gfForAmbient(Pressure ambientForDepth) and especially the comment jus5 above. This code at least appears to work and matches MultiDeco.

 

[BlueTrin]

Thank you.

About GF being a hack, I am quite pragmatic: the goal is to provide some margin and stay further away from the m-value lines.

And the GF methodology is achieving its goal in a fairly straightforward manner

 

[KenGordon]

Thank you.

About GF being a hack, I am quite pragmatic: the goal is to provide some margin and stay further away from the m-value lines.

And the GF methodology is achieving its goal in a fairly straightforward manner

It is ok, what I object to is the holding out of it as some kind of superior algorithm when really it is a very simple dissolved gas model with a very nasty kludge on top. Also it is often claimed to be an open standard, especially compared to the algorithms used by the majority of dive computer manufacturers, whereas really it has many gaps for the implementation to choose.

Remember the m value lines are just the model, at least they ought to be m value clouds, and possibly are quite unrelated to the real risk. If you have not already, read up on the impact of temperature at different stages of a dive. A quick google gives A surprise lesson… temperature effects on decompression diving - NEDU study

SB posters worship on the alter of Shearwater. It is a shame really as they are fine computers with an idiot fan base. Over the years compasses and air integration have gone from a really bad idea to absolutely essential as Shearwater have introduced them. Meanwhile everything else is regarded as complete rubbish. This, along with the bogus open assertions, means that any innovation which doesn’t come from Shearwater is dismissed. Aqualung have computers which will take heart rate into account, but according to SB that is worse than useless. Suunto, Mares and some others take the actual dive profile into account, apparently that is a disadvantage.

 

[KenGordon]

PS, on your graph there is a kink in the ceiling after a few minutes, can you tell why? I suppose it might be that which tissue is the limiting one, but I would have thought it would still be the fastest tissue limiting then.