Yilda statistik mexanika , an Ursell funktsiyasi yoki bog'liq korrelyatsiya funktsiyasi , a kumulyant a tasodifiy o'zgaruvchi . Uni ko'pincha ulangan holda yig'ish orqali olish mumkin Feynman diagrammalari (barcha Feynman diagrammalarining yig'indisi korrelyatsion funktsiyalar ).
Ursell funktsiyasi nomi berilgan Xarold Ursel , uni 1927 yilda kim kiritgan.
Ta'rif
Agar X tasodifiy o'zgaruvchidir lahzalar s n siz n X bilan bog'liq eksponent formula :
E ( tugatish ( z X ) ) = ∑ n s n z n n ! = tugatish ( ∑ n siz n z n n ! ) {displaystyle operator nomi {E} (exp (zX)) = sum _ {n} s_ {n} {frac {z ^ {n}} {n!}} = exp chap (sum _ {n} u_ {n} { frac {z ^ {n}} {n!}} ight)} (qayerda E {displaystyle operator nomi {E}} kutish ).
Ko'p o'zgaruvchan tasodifiy o'zgaruvchilar uchun Ursell funktsiyalari yuqoridagiga o'xshash tarzda va ko'p o'zgaruvchan kumulyantlar singari aniqlanadi.[1]
siz n ( X 1 , … , X n ) = ∂ ∂ z 1 ⋯ ∂ ∂ z n jurnal E ( tugatish ∑ z men X men ) | z men = 0 {displaystyle u_ {n} chap (X_ {1}, ldots, X_ {n} ight) = chap. {frac {qisman} {qisman z_ {1}}} cdots {frac {qisman} {qisman z_ {n}} } log operator nomi {E} chap (exp sum z_ {i} X_ {i} ight) ight | _ {z_ {i} = 0}} Bitta tasodifiy o'zgaruvchining Ursell funktsiyalari X sozlash orqali bulardan olinadi X = X 1 = … = X n
Birinchi bir necha tomonidan berilgan
siz 1 ( X 1 ) = E ( X 1 ) siz 2 ( X 1 , X 2 ) = E ( X 1 X 2 ) − E ( X 1 ) E ( X 2 ) siz 3 ( X 1 , X 2 , X 3 ) = E ( X 1 X 2 X 3 ) − E ( X 1 ) E ( X 2 X 3 ) − E ( X 2 ) E ( X 3 X 1 ) − E ( X 3 ) E ( X 1 X 2 ) + 2 E ( X 1 ) E ( X 2 ) E ( X 3 ) siz 4 ( X 1 , X 2 , X 3 , X 4 ) = E ( X 1 X 2 X 3 X 4 ) − E ( X 1 ) E ( X 2 X 3 X 4 ) − E ( X 2 ) E ( X 1 X 3 X 4 ) − E ( X 3 ) E ( X 1 X 2 X 4 ) − E ( X 4 ) E ( X 1 X 2 X 3 ) − E ( X 1 X 2 ) E ( X 3 X 4 ) − E ( X 1 X 3 ) E ( X 2 X 4 ) − E ( X 1 X 4 ) E ( X 2 X 3 ) + 2 E ( X 1 X 2 ) E ( X 3 ) E ( X 4 ) + 2 E ( X 1 X 3 ) E ( X 2 ) E ( X 4 ) + 2 E ( X 1 X 4 ) E ( X 2 ) E ( X 3 ) + 2 E ( X 2 X 3 ) E ( X 1 ) E ( X 4 ) + 2 E ( X 2 X 4 ) E ( X 1 ) E ( X 3 ) + 2 E ( X 3 X 4 ) E ( X 1 ) E ( X 2 ) − 6 E ( X 1 ) E ( X 2 ) E ( X 3 ) E ( X 4 ) {displaystyle {egin {aligned} u_ {1} (X_ {1}) = {} va operator nomi {E} (X_ {1}) u_ {2} (X_ {1}, X_ {2}) = {} va operator nomi {E} (X_ {1} X_ {2}) - operator nomi {E} (X_ {1}) operator nomi {E} (X_ {2}) u_ {3} (X_ {1}, X_ {2}, X_ {3}) = {} va operator nomi {E} (X_ {1} X_ {2} X_ {3}) - operator nomi {E} (X_ {1}) operator nomi {E} (X_ {2} X_ {3}) ) -operator nomi {E} (X_ {2}) operator nomi {E} (X_ {3} X_ {1}) - operator nomi {E} (X_ {3}) operator nomi {E} (X_ {1} X_ {2}) ) + 2operatorname {E} (X_ {1}) operatorname {E} (X_ {2}) operatorname {E} (X_ {3}) u_ {4} chap (X_ {1}, X_ {2}, X_ {3}, X_ {4} ight) = {} va operator nomi {E} (X_ {1} X_ {2} X_ {3} X_ {4}) - operator nomi {E} (X_ {1}) operator nomi {E} (X_ {2} X_ {3} X_ {4}) - operator nomi {E} (X_ {2}) operator nomi {E} (X_ {1} X_ {3} X_ {4}) - operator nomi {E} (X_ {3}) operator nomi {E} (X_ {1} X_ {2} X_ {4}) - operator nomi {E} (X_ {4}) operator nomi {E} (X_ {1} X_ {2} X_ {3}) ) & & - operator nomi {E} (X_ {1} X_ {2}) operator nomi {E} (X_ {3} X_ {4}) - operator nomi {E} (X_ {1} X_ {3}) operator nomi {E } (X_ {2} X_ {4}) - operator nomi {E} (X_ {1} X_ {4}) operator nomi {E} (X_ {2} X_ {3}) & + 2operatorname {E} (X_ {) 1} X_ {2}) o peratorname {E} (X_ {3}) operator nomi {E} (X_ {4}) + 2operatorname {E} (X_ {1} X_ {3}) operatorname {E} (X_ {2}) operatorname {E} ( X_ {4}) + 2operatorname {E} (X_ {1} X_ {4}) operatorname {E} (X_ {2}) operatorname {E} (X_ {3}) + 2operatorname {E} (X_ {2}) X_ {3}) operator nomi {E} (X_ {1}) operator nomi {E} (X_ {4}) & + 2operatorname {E} (X_ {2} X_ {4}) operator nomi {E} (X_ {1) }) operatorname {E} (X_ {3}) + 2operatorname {E} (X_ {3} X_ {4}) operatorname {E} (X_ {1}) operatorname {E} (X_ {2}) - 6operatorname { E} (X_ {1}) operator nomi {E} (X_ {2}) operator nomi {E} (X_ {3}) operator nomi {E} (X_ {4}) oxiri {hizalanmış}}} Xarakteristikasi
Perkus (1975) Ursell funktsiyalari, bir nechta tasodifiy o'zgaruvchilarning ko'p qirrali funktsiyalari sifatida qaralganda, o'zgaruvchilar har doim yo'q bo'lib ketishi bilan doimiygacha aniq aniqlanganligini ko'rsatdi. X men
Shuningdek qarang
Adabiyotlar
Glimm, Jeyms ; Jaffe, Artur (1987), Kvant fizikasi (2-nashr), Berlin, Nyu-York: Springer-Verlag , ISBN 978-0-387-96476-8 JANOB 0887102 Percus, J. K. (1975), "Ising spin panjaralari uchun o'zaro tengsizlik", Kom. Matematika. Fizika. , 40 (3): 283–308, Bibcode :1975CMaPh..40..283P , doi :10.1007 / bf01610004 , JANOB 0378683 , S2CID 120940116 Ursell, H. D. (1927), "Gibbsning nomukammal gazlar uchun fazali integralini baholash", Proc. Kembrij falsafasi. Soc. , 23 (6): 685–697, Bibcode :1927PCPS ... 23..685U , doi :10.1017 / S0305004100011191 
