Son of Deep Stops *or* Waiting to be merged with the mother thread...

[rossh]

If that's correct, the problem isn't the gradient factor which you are criticizing. It's its implementation in the programming.

Does it matter which? We have only one implementation of GF, and all programs need to agree with it. The current one is what causes all these GF inconsistent and exponential runaway issues. Nothing will get fixed until everyone faces up to this fact.

We currently have some people imagining that GF as some kind of gold standard perfect representation. Then they think anything less is not satisfactory. Reality is, GF as we have it now, its a big exponential growth error.


We can make a new one - with all those errors fixed. Or come up with something completely new.

 

[kensuf]

Oh boy, here we go again.

 

[Storker]

Does it matter which?

It most definitely does.

There's a fundamental difference between a sound model incorrectly implemented, and a fundamentally flawed model. The former should fairly easily be fixed, and an incorrect implementation shouldn't reflect on the soundness of a model.

 

[rossh]

It most definitely does.

There's a fundamental difference between a sound model incorrectly implemented, and a fundamentally flawed model. The former should fairly easily be fixed, and an incorrect implementation shouldn't reflect on the soundness of a model.

Agreed, but only if you want to fix it. The GF idea can be made to work properly, but NOT how its been implemented so far. What you have now, is a sequence of patched on the the end, exponentially growing errors.

Now to be fair, when Erik Baker first made this, and GF was being used sensibly, then the error in implementations did not matter, because the changes being asked of it, were small.

But now, its a joke - people want a 30% or 40% reduction, in a logarithmic value, and the errors that introduces cannot be over looked.


Go back to my diagram.

Current design - a patch onto the end of a plan is the wrong way to do it.

Solution - make GF part of the model parameters - solved.


In fact you are going to have to do that, because any new model design, will never naturally generate the first stops that you want. A dissolved model, of any kind, cannot make any real stop much deeper than the natural ZHL ones we have now.

Or to put it another way... the stops you so desire, are beyond the scope of a dissolved model. Therefore, you are compelled to a bubble model theory of some kind, whether you like it or not.


.

 

[lowviz]

Agreed, but only if you want to fix it. The GF idea can be made to work properly, but NOT how its been implemented so far. What you have now, is a sequence of patched on the end, exponentially growing errors. ...//...

I think that this can be best shown by looking at the stop times for a given depth dive vs. bottom time. See graph below.

I see a few interesting points from just looking at the "data". First, the degree of "exponentiality" differs with bottom time. Good luck with a linear correction across the board. Second, and unrelated to the first, is that the Navy Table 5 has the look and feel of experimental data. Look at the wonky 240 minute bottom time curve and right next to it is a lovely 180 minute bottom time curve.

So why can't one fit smooth curves to each of the bottom times series and then fit a surface to the lot? Conservatism would just be raising or lowering the entire surface by whatever floats your boat...

 

[lowviz]

I'll add the Excel sheet if anybody else wants to play:

 

[UWSojourner]

That diagram is the simple theory of GF. .... but, the reality, it was not implemented that way. there are more conditions and issues than shown above. The way its coded, is to be patched onto the end of a finished plan. It has compounding time problems, and gets into exponential runaway conditions.

I've coded GF in both desktop and real-time systems and VPM-B as well. Over the years you've posted misleading or completely false statements about GF. Your statement above is the latter.

The actual coding is like Storker posted. Here's an article describing GF.

Your statement that it "gets into exponential runaway conditions" implies that you have an independent standard used to make that assessment. What is it? I suspect you're just looking at VPM-B as the standard .

 

[cerich]

but aren't exponentials also a issue with VPM? Thus why you don't agree with anything past 5 rossh?

 

[UWSojourner]

Current design - a patch onto the end of a plan is the wrong way to do it.

That's good because that's not what GF does.

Although, your /E extension to VPM-B is clearly a patch onto the end of a VPM-B plan. People who live in glass houses shouldn't throw stones.

Solution - make GF part of the model parameters - solved.

I sense a new marketing campaign beginning.

In fact you are going to have to do that, because any new model design, will never naturally generate the first stops that you want. A dissolved model, of any kind, cannot make any real stop much deeper than the natural ZHL ones we have now.

If I want a first stop at a gradient factor of 50, then GF50/75 gives me the first stop I want. Solved.

Therefore, you are compelled to a bubble model theory of some kind, whether you like it or not.

The NEDU study tested 2 models in actual dive trials. The bubble model produced 5% DCS hits, the "dissolved model" produced 1.6% DCS hits. See here for comparison of the NEDU bubble model to VPM-B and the more successful gas-content model to GF.

Divers are not compelled to use bubble model theory. It would be better to use the information from closely controlled experiments that measure the effects and presence of actual bubbles -- because divers don't get bent theoretically, they actually get bent.

The current synthesis of available research leads to the conclusion that bubble-model-type deep stops have been oversold to the diving community. I guess the overselling continues.

 

[boulderjohn]

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A ScubaBoard Staff Message...

This is one of two threads that has been opened since the other thread was closed. I posted the following warning on the other one:

The reason the other thread was closed was because of the flurry of personal attacks. In some cases, posts that responded to other posts that had been deleted due to personal attacks had to be deleted as well because of the reference to a deleted posts. It was a very difficult process to separate the wheat from the chaff, and I sincerely hope that we can discuss this important topic while staying on the topic and not the individuals involved.

The concern is the fallacy of the ad hominem attack, in which the character of a person is attacked rather than the argument at issue. That sounds simple enough, but it is actually tricky, because not all personal attacks are fallacies. There are cases in which it is legitimate to question the credentials of an individual making a case, and it is possible to question the motives of a person making a case. For example, when Andrew Wakefield was shown to have a major financial interest in getting people to believe that autism was linked to vaccinations, it severely undermined his credibility by showing a motivation for misreporting data, which he also was shown to have done. With both of those problems clearly demonstrated, ad hominem comments became legitimate matters of discussion. (See the link in this paragraph for further discussion of this.)

In the previous thread, words like fake and phony were red flags because of the implication of an attack on an individual's character. If two people look at data and draw different conclusions, that is a disagreement, and one can question the legitimacy of an opposing interpretation. To say that a position is fake or phony, on the other hand, means that the other's position is a deliberate misrepresentation with the intent to deceive, and it is thus a personal attack. As stated in the last paragraph, if you have clear information showing that the opposing view is in fact a deliberate attempt to deceive, then that is a legitimate point, but you had better be able to prove that intent to the satisfaction of others, especially the moderators. If someone has accused you of such intent, you of course will have the right to respond.

Please be careful in this thread--don't make it personal!

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