On Mon, 6 Nov 2023 14:55:39 -0500
J C Nash wrote:
> However, I'm wondering if this approach is worth writing up, at least
> as a vignette or blog post. It does need a shorter example and some
> explanation of the "why" and some testing perhaps.
Do you mean using this problem as a basis to
G'day Troels,
On Tue, 7 Nov 2023 07:14:02 +0100
Troels Ring wrote:
> Be as it may, I wonder if not your method might work if only we KNOW
> that pK1 is either positive OR negative, in which case we have pK1 =
> -exp(theta1)?
If pK1 can be either negative or positive (or 0 :-) ), and it is just
Thanks a lot, Berwin. Unfortunately, pK1 may well be negative and as I
understand the literature it may be poorly defined as such, and also
seems to be at a boundary, since when lower is set to say rep(-4,3) pK1
is returned as -4 while pK2 and pK3 are undisturbed. Perhaps the point
is that pK1
G'day Troels,
On Mon, 6 Nov 2023 20:43:10 +0100
Troels Ring wrote:
> Thanks a lot! This was amazing. I'm not sure I see how the conditiion
> pK1 < pK2 < pK3 is enforced?
One way of enforcing such constraints (well, in finite computer
arithemtic only "<=" can be enforced) is to rewrite the
I won't send to list, but just to the two of you, as I don't have
anything to add at this time. However, I'm wondering if this approach
is worth writing up, at least as a vignette or blog post. It does need
a shorter example and some explanation of the "why" and some testing
perhaps.
If there's
Thanks a lot! This was amazing. I'm not sure I see how the conditiion
pK1 < pK2 < pK3 is enforced? - it comes from the derivation via
generalized Henderson-Hasselbalch but perhaps it is not really
necessary. Anyway, the use of Vectorize did the trick!
Best wishes
Troels
Den 06-11-2023 kl.
Your script is missing something (in particular kw).
I presume you are trying to estimate the pK values. You may have more success
with package nlsr than nls(). nlsr::nlxb() tries to get the Jacobian of the
model specified by a formula and do so by applying symbolic or automatic
differentiation.
В Mon, 6 Nov 2023 17:53:49 +0100
Troels Ring пишет:
> Hence I wonder if I could somehow have non linear regression to find
> the 3 pK values. Below is HEPESFUNC which delivers charge in the
> fluid for known pKs, HEPTOT and SID. Is it possible to have
> root-finding in the formula with nls?
Dear friends - I have a function for the charge in a fluid (water)
buffered with HEPES and otherwise only containing Na and Cl so that [Na]
- [Cl] = SID (strong ion difference) goes from -1 mM to 1 mM. With known
SID and total HEPES concentration I can calculate accurately the pH if I
know 3
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