What Is the Mathematical Substitution Used in This Integral Notation?

In summary, The conversation is discussing a step in the book "Applied analysis by Hilbert space method" where the author is showing that L(f)=-f'' is a hermitian operator. This step involves a substitution and some changes in notation, but the main idea is to show the relationship between L(f) and f''.
  • #1
Alesak
111
0
Hi,

in the book "Applied analysis by Hilbert space method", I have no idea what is happening in the last step here:

[itex]<L(f), g>=\int^{1}_{0} L(f)\overline{g}dx=-\int^{1}_{0} f''\overline{g}dx=-\int^{1}_{0}\overline{g} d(f')[/itex]

where L(f) = -f'' and both f and g are functions of x.

It seems like some kind of substitution is going on. But how can the author disappear f'', change dx and not change g(x) at the same time?


He is showing here that l(y)=-y'' is hermitian operator and this is first step.
 
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  • #2
f''=df'/dx
f''dx=df'
 

Related to What Is the Mathematical Substitution Used in This Integral Notation?

1. What is the purpose of using "weird" notation in integrals?

The "weird" notation in integrals, also known as Leibniz notation, is used to represent the derivative and integral of a function in a compact and intuitive way. It allows for easier calculation and visualization of the relationship between the function and its derivative or integral.

2. How is the "weird" notation different from traditional notation in integrals?

The "weird" notation, or Leibniz notation, uses the symbols dx and dy to represent the infinitesimal change in the independent and dependent variables, respectively. This is different from traditional notation, which uses the integral sign and the limits of integration to represent the area under the curve.

3. Is the "weird" notation more accurate than traditional notation in integrals?

No, both notations are equally accurate in representing the integral of a function. The choice of notation is a matter of personal preference and convenience.

4. Can the "weird" notation be used for all types of integrals?

Yes, the "weird" notation can be used for all types of integrals, including definite and indefinite integrals, as well as single and multiple integrals.

5. Are there any disadvantages to using the "weird" notation in integrals?

One potential disadvantage of the "weird" notation is that it can be confusing for beginners, as it requires a deeper understanding of the concept of infinitesimals. Additionally, it may not be suitable for certain types of integrals that involve complex functions.

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