Should I Use Total or Partial Differentiation in Absolute Error Calculation?

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Discussion Overview

The discussion revolves around the calculation of absolute error for a quantity defined as the product of two variables, specifically addressing whether to use total or partial differentiation in the differentiation process. The scope includes mathematical reasoning and conceptual clarification regarding differentiation techniques in error analysis.

Discussion Character

  • Mathematical reasoning, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant proposes that the absolute error of the quantity p, defined as p=a*b, should be calculated using differentiation of the logarithmic form.
  • Another participant suggests that it does not matter whether total or partial differentiation is used, as all forms (da, ∂a, Δa) represent the error in measuring a.
  • A question is raised about the correctness of using partial derivatives when differentiating a function of two variables.
  • One participant argues that using d is correct because it involves differentiating ln p with respect to p, independent of the dependencies of p.
  • A different method for calculating absolute errors is introduced, which involves the square root of the sum of the squares of the partial derivatives multiplied by the changes in the variables, claiming it gives the maximum change in the function for given changes in its arguments.

Areas of Agreement / Disagreement

Participants express differing views on whether total or partial differentiation should be used, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

The discussion includes assumptions about the definitions of errors and the context in which differentiation is applied, which may not be fully articulated. There are also unresolved mathematical steps regarding the application of differentiation techniques.

Chemist@
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The absolute error of the quantity p should be calculated.
p=a*b where a and b are two variables.
By taking ln on both sides:
lnp=lna+lnb, then differentiating:
dp/p=da/a+db/b
dp=abolute error
Should I have used total or partial differential in the differentiation step?
 
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Doesn't matter. [itex]da[/itex] or [itex]\partial a[/itex] or [itex]\Delta a[/itex], they all represent the error in measuring a.
 
Which is the most correct to use when I differentiate a function of two variables? Partial derivative?
 
Well, now that I think, [itex]d[/itex] is the correct one. Because you're actually differentiating [itex]\ln p[/itex] w.r.t. p regardless of what p depends on! The same for other two logarithms.
Anyway, I've heard several methods for calculating absolute errors. But the one I prefer, is the following:
[itex]E[f(x_1,x_2,...,x_n)]=\sqrt{\sum_{k=1}^n (\frac{\partial f}{\partial x_k} dx_k)^2}[/itex]
Because it obviously gives the maximum change in f for given changes in its arguments.
 

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