What Is the Mathematical Substitution Used in This Integral Notation?

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SUMMARY

The integral notation discussed involves the operator L(f) defined as L(f) = -f''. The transformation shown in the equation =\int^{1}_{0} L(f)\overline{g}dx=-\int^{1}_{0} f''\overline{g}dx=-\int^{1}_{0}\overline{g} d(f') demonstrates a mathematical substitution where the second derivative f'' is replaced by its differential form df' while maintaining the function g unchanged. This substitution is crucial for proving that the operator L is Hermitian, as indicated by the relationship l(y)=-y''. The discussion highlights the importance of understanding differential operators in the context of functional analysis.

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Alesak
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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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f''=df'/dx
f''dx=df'
 

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