Generalized Ordinary Differential Equations in Abstract Spaces and Applications. Группа авторов

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Generalized Ordinary Differential Equations in Abstract Spaces and Applications - Группа авторов

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t right-parenthesis phi left-parenthesis t right-parenthesis"/>

      holds (see Theorem 1.53). Hence, f element-of upper R left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis subset-of upper K left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis.

      Consider the indefinite integral ModifyingAbove f With tilde left-parenthesis t right-parenthesis equals integral Subscript 0 Superscript t Baseline f left-parenthesis r right-parenthesis d r, t element-of left-bracket 0 comma 1 right-bracket, of f. Then,

left-parenthesis integral Subscript 0 Superscript t Baseline f left-parenthesis r right-parenthesis d r right-parenthesis left-parenthesis s right-parenthesis equals left-parenthesis integral Subscript 0 Superscript t Baseline chi Subscript left-bracket r comma 1 right-bracket Baseline d r right-parenthesis left-parenthesis s right-parenthesis equals integral Subscript 0 Superscript t Baseline chi Subscript left-bracket r comma 1 right-bracket Baseline left-parenthesis s right-parenthesis d r equals integral Subscript 0 Superscript t logical-and s Baseline d r equals t logical-and s

      and, hence,

ModifyingAbove f With tilde left-parenthesis t right-parenthesis left-parenthesis s right-parenthesis equals t logical-and s equals inf left-brace right-brace comma t comma s period

      Thus, f overTilde is absolutely continuous.

      On the other hand, f overTilde is nowhere differentiable (see [73], Example 3.1). Then, the Lebesgue theorem implies f not-an-element-of script upper L 1 left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis, where by script upper L 1 left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis, we denote the space of functions from left-bracket 0 comma 1 right-bracket to upper X which are Lebesgue integrable with finite integral. See the appendix of this chapter. As a matter of fact, the Fundamental Theorem of Calculus for the Henstock integral (see Theorem 1.73) yields that f not-an-element-of upper H left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis. Optionally, one can verify that f not-an-element-of upper H left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis simply by noticing that

vertical-bar vertical-bar vertical-bar vertical-bar minus minus times times of ff left-parenthesis right-parenthesis xi i left-parenthesis right-parenthesis minus minus tit minus minus i 1 integral integral t minus minus i 1 ti of ff left-parenthesis right-parenthesis t separator d separator t greater-than-or-slanted-equals one half left-parenthesis t Subscript i Baseline minus t Subscript i minus 1 Baseline right-parenthesis comma

      for every left-parenthesis xi Subscript i Baseline comma left-bracket t Subscript i minus 1 Baseline comma t Subscript i Baseline right-bracket right-parenthesis element-of upper T upper D Subscript left-bracket 0 comma 1 right-bracket.

      Claim. f element-of italic RMS left-parenthesis left-bracket 0 comma 1 right-bracket comma upper X right-parenthesis, that is, f is Riemann–McShane integrable (see the appendix of this chapter).

      Is is sufficient to prove that, given epsilon greater-than 0, we can find delta greater-than 0 such that for every delta-fine d equals left-parenthesis xi Subscript i Baseline comma left-bracket t Subscript i minus 1 Baseline comma t Subscript i Baseline right-bracket right-parenthesis element-of upper S upper T upper D Subscript left-bracket 0 comma 1 right-bracket (the reader may want to check the notation upper S upper T upper D Subscript left-bracket a comma b right-bracket in the appendix of this chapter),

vertical-bar vertical-bar vertical-bar vertical-bar minus minus of ff tilde left-parenthesis right-parenthesis 1 sigma-summation sigma-summation equals equals i 1 vertical-bar vertical-bar d times times of ff left-parenthesis right-parenthesis xi i left-parenthesis right-parenthesis minus minus tit minus minus i 1 less-than epsilon period

       If and , then . Therefore, and, hence,

       If and , then . Therefore,and we obtain

      Finally, we get

StartLayout 1st Row 1st Column vertical-bar vertical-bar vertical-bar vertical-bar minus minus of ff tilde left-parenthesis right-parenthesis 1 sigma-summation sigma-summation equals equals i 1 vertical-bar vertical-bar d times times of ff left-parenthesis right-parenthesis xi i left-parenthesis right-parenthesis minus minus tit minus minus i 1 Subscript infinity Baseline equals 2nd Column sup Underscript 0 less-than-or-slanted-equals s less-than-or-slanted-equals 1 Endscripts StartAbsoluteValue ModifyingAbove f With tilde left-parenthesis 1 right-parenthesis left-parenthesis s right-parenthesis minus sigma-summation Underscript i equals 1 Overscript StartAbsoluteValue d EndAbsoluteValue Endscripts f left-parenthesis xi Subscript i Baseline right-parenthesis left-parenthesis s right-parenthesis left-parenthesis t Subscript i Baseline minus t Subscript i minus 1 Baseline right-parenthesis EndAbsoluteValue 2nd Row 1st Column equals 2nd Column sup Underscript 0 less-than-or-slanted-equals s less-than-or-slanted-equals 1 Endscripts StartAbsoluteValue s minus sigma-summation Underscript xi Subscript i Baseline less-than-or-slanted-equals s Endscripts left-parenthesis t Subscript i Baseline minus t Subscript i minus 1 Baseline right-parenthesis EndAbsoluteValue less-than 
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