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Controllability of Single-valued Chapter | 7  195


                        t          Ð t         ε  ^        Ð  t
                       Ð
                yðtÞ  5  S α ðsÞx 1 ds 1  S α ðt 2 sÞBu ðs; φ 1 yÞds 1  S α ðt 2 sÞfðsÞds
                        0           0                       0

                       Ð  t      Ð s     ^
                     1   S α ðt 2 sÞ  σðs; τ; φ 1 y τ ÞdWðτÞ ds; tAJ; fAN F;x
                        0         0       τ
             where
                                              n
                 ε  ^                     b 21       Ð  b  ~

                u ðs; φ 1 yÞ 5 B S ðb 2 sÞðEI1Π Þ  E~ x b 1  0  φðsÞdWðsÞ 2 S α ðbÞφð0Þ
                              α
                                          0
                           2  Ð  b  S α ðsÞx 1 ds 2  Ð b  S α ðb 2 sÞfðsÞds
                              0           0
                                         Ð  s                o
                                                ^
                              b
                             Ð
                           2   S α ðb 2 sÞ  σðs; τ; φ 1 y τ ÞdWðτÞ ds ; fAN F;x :
                              0          0       τ
                                                   0
                    0
                Set B 5 fyAB b ; y 0 5 0ABg. For any yAB , we have
                    b
                                                   b
                                                   1               1

                      OyO b 5 Oy 0 O B 1 sup EOyðsÞO 2 2  5 sup EOyðsÞO 2 2
                                    sA½0;bŠ          sA½0;bŠ
                   0
             thus ðB ; OUO b Þ is a Banach space.
                   b
                                                   0
                                                         2
                For any positive number r, set B r 5 fyAB : OyO # rg, then for each r,
                                                   b     b
                                                   0
             B r is clearly a bounded closed convex set in B , and for yAB r , we have
                                                   b
                   ^  2        2   ^  2
              Oy t 1 φ O # 2ðOy t O 1 Oφ O Þ
                    t B        B    t B

                                                             ^
                                                                      ^
                                                                 2
                                                2
                                         2
                       # 4 sup     EOyðsÞO 1 Oy 0 O 1 sup  EOφðsÞO 1 Oφ O 2
                              sA½0;tŠ           B     sA½0;tŠ          0 B
                                2 2ωb      2        2
                       # 4 r 1 M e  EOφð0ÞO   1 4OφO 5 4r 1 r ;

                                           H        B
                                    2
                                            2
                         2 2ωb

             where r 5 4M e  EOφð0ÞO 1 4OφO .
                                    H       B
                                         0
                                                0
                                                                   0
                Define the multivalued map Ψ:B -PðB Þ by Ψy the set of ρAB such that
                                         b      b                  b
                     8
                       0; tAð2N; 0Š
                     >
                     >
                       Ð  t        Ð t                     Ð  t
                     <                         ε  ^
                ρðtÞ 5  0  S α ðsÞx 1 ds 1  0  S α ðt 2 sÞBu ðs; φ 1 yÞds 1  0  S α ðt 2 sÞfðsÞds

                     >
                     >     Ð  t      Ð  s   ^
                     :  1   S α ðt 2 sÞ  σðs; τ; φ 1 y τ ÞdWðτÞ ds; tAJ
                           0          0      τ
                                              ε
             where fAN F;x . Obviously the operator Φ has a fixed point if and only if the
             operator Ψ has a fixed point.
                Step 1: For each yAB r ; Ψ is convex.
                Let ρ ; ρ AΨy then there exist f 1 ; f 2 AN F;x such that for each tAJ,
                        2
                     1
             one has
                                                  ^
                                              ε
                ρ ðtÞ 5  Ð 0 t  S α ðsÞx 1 ds 1  Ð 0 t  S α ðt 2 sÞBu ðs; φ 1 yÞds 1  Ð 0 t  S α ðt 2 sÞf i ðsÞds
                 i

                        Ð  t      Ð  s    ^
                      1   S α ðt 2 sÞ  σðs; τ; φ 1 y τ ÞdWðτÞ ds; i 5 1; 2:
                         0         0       τ
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