численные методыА.Б. САМОХИН, В.В. ЧЕРДЫНЦЕВ, А.А. ВОРОНЦОВ
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ɉɨɞɫɬɚɜɥɹɹ ɤɨɷɮɮɢɰɢɟɧɬɵ ɜ P |
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ɩɨɥɢɧɨɦ ɩɪɟɞɫɬɚɜɥɟɧ ɜ ɜɢɞɟ |
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ɫɭɦɦɵ ɞɜɭɯ ɥɢɧɟɣɧɵɯ ɮɭɧɤɰɢɣ ɧɟɡɚɜɢɫɹɳɢɯ ɨɬ ɨɪɞɢɧɚɬ ɭɦɧɨ ɠɟɧɧɵɯ ɧɚ ɨɪɞɢɧɚɬɵ ɢ ɨɛɥɚɞɚɸɳɢɯ ɫɜɨɣɫɬɜɨɦ
P (x ) y 1 y 0, P (x ) y 0 y 1. |
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ȼ ɷɬɨɦ ɫɨɫɬɨɢɬ ɢɞɟɹ ɩɨɫɬɪɨɟɧɢɹ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ Ʌɚɝɪɚɧɠɚ Ⱦɥɹ ɩɪɨɢɡɜɨɥɶɧɨɝɨ ɡɧɚɱɟɧɢɹ n ɡɚɩɢɲɟɦ ɢɧɬɟɪɩɨɥɹɰɢ ɨɧɧɵɣ ɩɨɥɢɧɨɦ ɜ ɜɢɞɟ
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Pn (x) |
y0 L0 (x) y1L1(x) ... yn Ln (x), |
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ɝɞɟ Li |
ɩɨɥɢɧɨɦɵ ɫɬɟɩɟɧɢ ɧɟ ɜɵɲɟ n, ɧɟ ɡɚɜɢɫɹɳɢɟ ɨɬ ɨɪɞɢɧɚɬ ɢ |
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ɨɛɥɚɞɚɸɳɢɟ |
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ɂɡ ɪɚɜɟɧɫɬɜɚ Li (x j ) |
0 ɫɥɟɞɭɟɬ ɱɬɨ Li ɢɦɟɟɬ n ɤɨɪɧɟɣ ɪɚɫɫɦɚɬ |
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ɪɢɜɚɸɬɫɹ ɨɞɧɨɤɪɚɬɧɵɟ ɤɨɪɧɢ |
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ɝɞɟ Ni — ɤɨɷɮɮɢɰɢɟɧɬ ɤɨɬɨɪɵɣ ɧɚɯɨɞɢɬɫɹ ɢɡ ɭɫɥɨɜɢɹ Li (xi ) |
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ȼ ɪɟɡɭɥɶɬɚɬɟ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ Ʌɚɝɪɚɧɠɚ ɢɦɟɟɬ ɜɢɞ |
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P (x) |
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(x x0 )(x x1)...(x xi 1)(x xi 1)...(x xn ) |
. (2.2.1) |
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Ⱦɨɫɬɨɢɧɫɬɜɚ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ Ʌɚɝɪɚɧɠɚ ɹɜɥɹɟɬɫɹ ɩɪɨɫɬɨɬɚ ɤɨɧɫɬɪɭɤɰɢɢ ɉɪɢ ɡɚɞɚɧɧɨɦ ɧɚɛɨɪɟ ɚɛɫɰɢɫɫ ɭɡɥɨɜɵɯ ɬɨ
ɱɟɤ ɢ ɜɵɛɪɚɧɧɨɣ ɪɚɫɱɟɬɧɨɣ ɬɨɱɤɟ x* ɭɩɪɨɳɚɟɬɫɹ ɜɵɱɢɫɥɟɧɢɹ ɞɥɹ ɪɚɡɥɢɱɧɵɯ ɨɪɞɢɧɚɬ yi ɇɟɞɨɫɬɚɬɨɤ — ɞɨɛɚɜɥɟɧɢɟ n+1)-ɨɝɨ ɭɡɥɚ
(xn 1, yn 1) ɬɪɟɛɭɟɬ ɩɟɪɟɪɚɫɱɟɬɚ ɜɫɟɯ ɫɥɚɝɚɟɦɵɯ
ɉɨɝɪɟɲɧɨɫɬɶ ɜɵɱɢɫɥɟɧɢɹ ɩɭɫɬɶ f (x) — ɮɭɧɤɰɢɹ, ɞɢɮɮɟɪɟɧ ɰɢɪɭɟɦɚɹ n+1 ɪɚɡ, ɢ Pn (x) — ɩɪɢɛɥɢɠɚɸɳɢɣ ɟɺ ɢɧɬɟɪɩɨɥɹɰɢɨɧ ɧɵɣ ɩɨɥɢɧɨɦ
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ɝɞɟ M n 1 max |
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ɂɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ Ʌɚɝɪɚɧɠɚ ɩɪɢ ɥɢɧɟɣɧɵɯ ɩɪɟɨɛ ɪɚɡɨɜɚɧɢɹɯ x = at + b (t — ɧɨɜɚɹ ɩɟɪɟɦɟɧɧɚɹ ɫɨɯɪɚɧɹɟɬ ɫɜɨɣ ɜɢɞ
ɂɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ ɇɶɸɬɨɧɚ
ɉɭɫɬɶ n ɬɨɝɞɚ P0 (x) y0 ɟɫɥɢ n = ɬɨ ɜɵɪɚɠɟɧɢɟ ɞɥɹ ɩɨ
ɥɢɧɨɦɚ ɦɨɠɧɨ ɡɚɩɢɫɚɬɶ ɜ ɜɢɞɟ P (x) |
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ɜɟɞɟɧɢɟ ɩɪɢɛɥɢɠɚɸɳɟɣ ɮɭɧɤɰɢɢ ɫ ɞɨɛɚɜɥɟɧɢɟɦ ɭɡɥɨɜ ɭɬɨɱɧɹɟɬ ɫɹ ɜɛɥɢɡɢ ɬɨɱɤɢ ɯ0 Ʉɨɧɫɬɪɭɤɰɢɹ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ ɇɶɸɬɨɧɚ ɬɚɤɨɜɚ
Pn (x) a0 a1(x x0 ) a2 (x x0 )(x x1) a3 (x x0 )(x x1)(x x2 )
an (x x0 )(x x1) (x xn 1).
Ɋɚɫɫɦɚɬɪɢɜɚɟɬɫɹ ɪɚɜɧɨɦɟɪɧɚɹ ɫɟɬɤɚ ɬ ɟ xi x0 ih .
Ⱦɥɹ ɞɚɥɶɧɟɣɲɟɝɨ ɚɧɚɥɢɡɚ ɜɜɨɞɢɬɫɹ ɩɨɧɹɬɢɟ ɤɨɧɟɱɧɨɣ ɪɚɡɧɨ ɫɬɢ Ʉɨɧɟɱɧɨɣ ɪɚɡɧɨɫɬɶɸ ɩɟɪɜɨɝɨ ɩɨɪɹɞɤɚ ɧɚɡɵɜɚɟɬɫɹ ɜɟɥɢɱɢɧɚ
'y(x) y(x h) y(x), x [x0 , xn ].
Ʉɨɧɟɱɧɚɹ ɪɚɡɧɨɫɬɶ ɜɬɨɪɨɝɨ ɩɨɪɹɞɤɚ ɨɩɪɟɞɟɥɹɟɬɫɹ ɩɨ ɩɟɪɜɨɣ
'2 y(x) 'y(x h) 'y(x) y(x 2h) 2 y(x h) y(x)
ɢ ɬ ɞ , ɤɨɧɟɱɧɚɹ ɪɚɡɧɨɫɬɶ i-ɝɨ ɩɨɪɹɞɤɚ ɨɩɪɟɞɟɥɹɟɬɫɹ ɱɟɪɟɡ ɪɟɤɭɪ ɪɟɧɬɧɨɟ ɫɨɨɬɧɨɲɟɧɢɟ
'(i 1) y(x) |
'(i) y(x h) '(i) y(x) |
ɢ ɡɚɜɢɫɢɬ ɨɬ ɡɧɚɱɟɧɢɣ y ɜ i + 1)-ɣ ɬɨɱɤɟ |
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ȼɵɪɚɠɟɧɢɟ ɜɢɞɚ x[n] |
x(x h)(x 2h) (x (n 1)h) ɧɚɡɵɜɚɟɬ |
ɫɹ ɨɛɨɛɳɟɧɧɵɦ ɩɪɨɢɡɜɟɞɟɧɢɟɦ ȿɝɨ ɩɟɪɜɚɹ ɤɨɧɟɱɧɚɹ ɪɚɡɧɨɫɬɶ ɪɚɜɧɚ
'x[n] (x h)[n] x[n] (x h)x(x h)...
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...(x (n 2)h) x(x h)(x 2h)...(x (n 1)h) nhx[n 1] . (2.3.1)
Ɉɬɫɸɞɚ ɫɥɟɞɭɟɬ ɜɵɪɚɠɟɧɢɟ ɞɥɹ ɤɨɧɟɱɧɵɯ ɪɚɡɧɨɫɬɟɣ ɞɥɹ ɨɛɨɛ ɳɟɧɧɨɝɨ ɩɪɨɢɡɜɟɞɟɧɢɹ ɜɵɫɲɢɯ ɩɨɪɹɞɤɨɜ
ɉɨɞɫɬɚɜɥɹɹ x0 ɜ Pn (x) ɩɨɥɭɱɢɦ a0 Pn (x0 ) y0 Ⱦɚɥɟɟ ɨɩɪɟ ɞɟɥɢɦ ɤɨɧɟɱɧɭɸ ɪɚɡɧɨɫɬɶ ɜ ɬɨɱɤɟ x0 ɂɡ ɫɜɨɣɫɬɜɚ ɩɨɥɭɱɢɦ
'Pn (x) |x x0 |
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Ɉɬɫɸɞɚ ɫɥɟɞɭɟɬ ɱɬɨ a |
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ɜɵɪɚɠɟɧɢɟ ɞɥɹ ɤɨɧɟɱɧɨɣ ɪɚɡɧɨɫɬɢ ɜɬɨɪɨɝɨ ɩɨɪɹɞɤɚ ɜ ɬɨɱɤɟ x0 :
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Ɉɛɳɚɹ ɮɨɪɦɭɥɚ ɢɦɟɟɬ ɫɥɟɞɭɸɳɢɣ ɜɢɞ a |
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ȼ ɪɟɡɭɥɶɬɚɬɟ ɩɨɥɭɱɚɟɦ ɩɟɪɜɵɣ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ ɇɶɸɬɨɧɚ
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ɉɨɫɬɪɨɟɧɧɵɣ ɬɚɤɢɦ ɨɛɪɚɡɨɦ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ ɩɪɨɯɨɞɢɬ ɱɟɪɟɡ ɭɡɥɨɜɵɟ ɬɨɱɤɢ
ȼɬɨɪɨɣ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ ɇɶɸɬɨɧɚ ɩɨɡɜɨɥɹɟɬ ɧɚ ɱɚɬɶ ɢɧɬɟɪɩɨɥɹɰɢɸ ɫ ɬɨɱɤɢ xn ɬ ɟ ɭɥɭɱɲɢɬɶ ɬɨɱɧɨɫɬɶ ɩɪɢɛɥɢɠɟ
ɧɢɹ ɧɚ ɩɪɚɜɨɣ ɝɪɚɧɢɰɟ ɢɧɬɟɪɜɚɥɚ ɢɧɬɟɪɩɨɥɹɰɢɢ
Pn (x) a0 a1(x xn ) a2 (x xn 1)(x xn )
a3 (x xn 2 )(x xn 1)(x xn ) an (x x1)(x xn 1) (x xn ).
ɂɡ ɫɬɪɭɤɬɭɪɵ ɩɨɥɢɧɨɦɚ ɫɥɟɞɭɟɬ ɱɬɨ a0 yn .
'Pn (xn 1) |x x |
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ɢ ɬɚɤ ɞɚɥɟɟ Ɉɤɨɧɱɚɬɟɥɶɧɨ ɩɨɥɭɱɢɦ |
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ɉɪɢ ɪɚɫɱɺɬɚɯ ɢ ɚɥɝɨɪɢɬɦɢɡɚɰɢɢ ɜɵɱɢɫɥɟɧɢɹ ɢɧɬɟɪɩɨɥɹɰɢɨɧ ɧɨɝɨ ɩɨɥɢɧɨɦɚ ɩɪɢɦɟɧɹɟɬɫɹ ɬɚɛɥɢɰɚ ɤɨɧɟɱɧɵɯ ɪɚɡɧɨɫɬɟɣ
Ɍɚɛɥɢɰɚ
ʋ |
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Ⱦɥɹ ɩɨɫɬɪɨɟɧɢɹ -ɝɨ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ ɇɶɸɬɨɧɚ ɧɟɨɛɯɨɞɢɦɚ -ɹ ɫɬɪɨɤɚ ɬɚɛɥ Ⱦɥɹ ɩɨɫɬɪɨɟɧɢɹ -ɝɨ ɢɧɬɟɪɩɨɥɹ ɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ ɇɶɸɬɨɧɚ ɧɟɨɛɯɨɞɢɦɚ ɩɨɛɨɱɧɚɹ ɞɢɚɝɨɧɚɥɶ ɬɚɛɥɢɰɵ Ɉɛɵɱɧɨ ɩɪɢ ɦɚɲɢɧɧɵɯ ɪɚɫɱɺɬɚɯ ɦɚɫɫɢɜ ɨɪɞɢɧɚɬ ɭɡɥɨ ɜɵɯ ɬɨɱɟɤ ɩɨɫɥɟɞɨɜɚɬɟɥɶɧɨ ɩɪɟɨɛɪɚɡɭɟɬɫɹ ɜ ɦɚɫɫɢɜ ɤɨɷɮɮɢɰɢɟɧ ɬɨɜ ai ɬɚɤ, ɱɬɨ ɨɧɢ ɡɚɩɨɦɢɧɚɸɬɫɹ ɜ ɫɨɨɬɜɟɬɫɬɜɭɸɳɢɯ ɷɥɟɦɟɧɬɚɯ
ɦɚɫɫɢɜɚ
ɉɪɢɦɟɪɵ ɢ ɡɚɞɚɧɢɹ ɞɥɹ ɩɪɚɤɬɢɱɟɫɤɢɯ ɡɚɧɹɬɢɣ
ɉɪɢɦɟɪ. Ⱦɚɧɚ ɬɚɛɥɢɰɚ ɭɡɥɨɜ ɉɨɫɬɪɨɢɬɶ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨ ɥɢɧɨɦ Ʌɚɝɪɚɧɠɚ ɢ ɩɪɨɜɟɫɬɢ ɩɪɨɜɟɪɤɭ ɬɚɛɥ
Ɍɚɛɥɢɰɚ
N |
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0,5 |
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3 |
1 |
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ȼ ɜɵɪɚɠɟɧɢɟ ɞɥɹ n=3 |
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P (x) |
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(x x1)(x x2 )(x x3 ) |
y |
(x x0 )(x x2 )(x x3 ) |
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3 |
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0 (x x )(x x )(x x ) |
1 (x x )(x x )(x x ) |
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0 |
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3 |
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y2 |
(x x0 )(x x1)(x x3 ) |
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y3 |
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(x x0 )(x x1)(x x2 ) |
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(x x )(x x )(x x ) |
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ɧɟɨɛɯɨɞɢɦɨ ɩɨɞɫɬɚɜɢɬɶ ɞɚɧɧɵɟ ɢɡ ɬɚɛɥ :
P (x) |
1(x 0,5)(x 1)(x 1,5) 2 |
(x 0)(x 1)(x 1,5) |
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3 |
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(0 0,5)(0 1)(0 1,5) |
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(0,5 0)(0,5 1)(0,5 1,5) |
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3 |
(x 0)(x 0,5)(x 1,5) |
1 |
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(x 0)(x 0,5)(x 1) |
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(1 0)(1 0,5)(1 1,5) |
(1,5 0)(1,5 0,5)(1,5 1) |
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ɉɨɫɥɟ ɩɪɟɨɛɪɚɡɨɜɚɧɢɣ ɩɨɥɭɱɢɦ P (x) 4x3 6x2 |
1. |
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ɉɪɨɜɟɪɤɚ: |
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3 |
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P3 |
(x0 ) |
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P3 (0) |
1 { y0 , P3 (x1) |
P3 (0,5) |
4 / 8 6 / 4 1 |
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2 { y1, |
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P3 |
(x2 ) |
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P3 (1) |
4 6 1 |
3 { y2 , |
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P3 |
(x3 ) |
P3 (1,5) |
4 27 / 8 6 9 / 4 1 |
1 { y3. |
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ɉɪɢɦɟɪ ɉɨɫɬɪɨɢɬɶ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɟ ɩɨɥɢɧɨɦɵ ɇɶɸɬɨɧɚ ɩɨ ɩɪɟɞɵɞɭɳɟɣ ɬɚɛɥɢɰɟ ɭɡɥɨɜɵɯ ɬɨɱɟɤ
ɉɟɪɜɵɣ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢ
ʋ |
x |
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y |
'y |
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'2 y |
'3y |
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ɧɨɦ ɇɶɸɬɨɧɚ |
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P (x) |
y 'y |
(x x ) |
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0,5 |
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(x x0 )(x x1) |
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2h2 |
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'3 y0 (x x0 )(x x1)(x x2 ); 6h3
P3 (x) 1 2x 0 |
3 |
x(x 0,5)(x 1) |
1 2x |
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6(0,5)3 |
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4(x3 1,5x2 0,5) 4x3 6x2 1.
16
ȼɬɨɪɨɣ ɢɧɬɟɪɩɨɥɹɰɢɨɧɧɵɣ ɩɨɥɢɧɨɦ ɇɶɸɬɨɧɚ
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'2 y |
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'3 y |
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P (x) |
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(x x ) |
1 (x x )(x x ) |
0 (x x )(x x )(x x ); |
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3 |
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2h2 |
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6h3 |
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P (x) |
1 2 |
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(x 1,5)(x 1) |
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(x 1,5)(x 1)(x 0,5) 4x3 6x2 1. |
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ȼɚɪɢɚɧɬɵ ɡɚɞɚɸɬɫɹ ɩɨ ɧɨɦɟɪɚɦ ɫɬɨɥɛɰɨɜ ɬɚɛɥ ɢ ɜ ɜɢɞɟ |
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ɞɪɨɛɟɣ |
N y |
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ɧɚɩɪɢɦɟɪ |
9 |
ɨɡɧɚɱɚɟɬ ɱɬɨ ɞɥɹ ɭɡɥɨɜɵɯ ɬɨɱɟɤ ɩɨ ɯ ɢ |
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ɭ ɜɵɛɢɪɚɸɬɫɹ ɞɟɜɹɬɵɣ ɢ ɜɬɨɪɨɣ ɜɚɪɢɚɧɬɵ ɫɨɨɬɜɟɬɫɬɜɟɧɧɨ Ʉɚɠ ɞɵɣ ɫɬɭɞɟɧɬ ɞɨɥɠɟɧ ɩɨɥɭɱɢɬɶ ɬɪɢ ɬɚɤɢɯ ɞɪɨɛɢ ɞɥɹ ɪɚɫɱɟɬɚ ɢɧ ɬɟɪɩɨɥɹɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ Ʌɚɝɪɚɧɠɚ ɩɟɪɜɨɝɨ ɢ ɜɬɨɪɨɝɨ ɢɧɬɟɪ ɩɨɥɹɰɢɨɧɧɨɝɨ ɩɨɥɢɧɨɦɚ ɇɶɸɬɨɧɚ Ɋɟɡɭɥɶɬɚɬ ɧɟɨɛɯɨɞɢɦɨ ɩɪɟɞɫɬɚ
ɜɢɬɶ ɜ ɜɢɞɟ P3 (x) a0 a1x a2 x2 a3 x3 ɝɞɟ ɤɨɷɮɮɢɰɢɟɧɬɵ ɩɪɚ
ɜɢɥɶɧɵɟ ɢɥɢ ɧɟɩɪɚɜɢɥɶɧɵɟ ɞɪɨɛɢ ɧɟ ɞɟɫɹɬɢɱɧɵɟ. ɉɪɨɜɟɪɤɚ ɩɪɨ ɢɡɜɨɞɢɬɫɹ ɩɨɞɫɬɚɧɨɜɤɨɣ ɭɡɥɨɜɵɯ ɬɨɱɟɤ
Ɍɚɛɥɢɰɚ
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ȼɚɪɢɚɧɬɵ Nx |
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n |
1 |
2 |
3 |
0 |
0 |
-0,5 |
-1 |
1 |
0,5 |
0 |
-0,5 |
2 |
1 |
0,5 |
0 |
3 |
1,5 |
1 |
0,5 |
Ɍɚɛɥɢɰɚ
n |
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ȼɚɪɢɚɧɬɵ N y |
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-1 |
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1 |
1 |
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-2 |
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-1 |
-1 |
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1 |
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0 |
2 |
1 |
1 |
-1 |
-1 |
-1 |
-1 |
-2 |
-1 |
-1 |
2 |
2 |
2 |
-1 |
0 |
-1 |
-1 |
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3 |
1 |
0 |
1 |
2 |
2 |
2 |
1 |
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1 |
-1 |
1 |
-2 |
1 |
2 |
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-1 |
2 |
17
ɑɂɋɅȿɇɇɕȿ ɆȿɌɈȾɕ ɊȿɒȿɇɂɃ ɌɊȺɇɋɐȿɇȾȿɇɌɇɕɏ ɂ ȺɅȽȿȻɊȺɂɑȿɋɄɂɏ ɍɊȺȼɇȿɇɂɃ
Ɉɛɳɢɣ ɜɢɞ ɭɪɚɜɧɟɧɢɹ f (x) 0 Ɋɟɲɢɬɶ ɭɪɚɜɧɟɧɢɟ ɬ ɟ ɧɚɣɬɢ ɟɝɨ ɤɨɪɟɧɶ ɨɡɧɚɱɚɟɬ ɨɩɪɟɞɟɥɢɬɶ x* ɬɚɤɨɟ ɱɬɨ f (x* ) { 0 .
ȼɨ ɦɧɨɝɢɯ ɫɥɭɱɚɹɯ ɬɨɱɧɨɟ ɡɧɚɱɟɧɢɟ x* ɧɚɣɬɢ ɧɟɜɨɡɦɨɠɧɨ ɩɨ ɷɬɨɦɭ ɢɫɩɨɥɶɡɭɸɬɫɹ ɩɪɢɛɥɢɠɟɧɧɵɟ ɦɟɬɨɞɵ ɤɨɝɞɚ ɡɧɚɱɟɧɢɟ ɤɨɪɧɹ ɨɩɪɟɞɟɥɹɟɬɫɹ ɫ ɡɚɞɚɧɧɨɣ ɬɨɱɧɨɫɬɶɸ H Ƚɟɨɦɟɬɪɢɱɟɫɤɢ ɤɨɪɟɧɶ – ɷɬɨ ɩɟɪɟɫɟɱɟɧɢɟ ɝɪɚɮɢɤɨɦ ɮɭɧɤɰɢɢ f (x) ɨɫɢ x .
Ɂɚɞɚɱɚ ɞɟɥɢɬɫɹ ɧɚ ɷɬɚɩɚ 1. Ʌɨɤɚɥɢɡɚɰɢɹ ɤɨɪɧɹ – ɬ ɟ ɧɚɯɨɠɞɟɧɢɟ ɢɧɬɟɪɜɚɥɚ ɧɚ ɤɨɬɨɪɨɦ
ɢɡɨɥɢɪɨɜɚɧ ɟɞɢɧɫɬɜɟɧɧɵɣ ɧɭɠɧɵɣ ɧɚɦ ɤɨɪɟɧɶ ȼɵɛɨɪ ɢɧɬɟɪɜɚɥɚ ɩɪɨɢɡɜɨɞɢɬɫɹ ɩɭɬɟɦ ɚɧɚɥɢɡɚ ɡɧɚɤɚ f (x) ɜ ɪɹɞɟ ɩɪɨɛɧɵɯ ɬɨɱɟɤ ɗɬɨɬ ɩɪɨɰɟɫɫ ɜ ɨɛɳɟɦ ɜɢɞɟ ɧɟ ɚɥɝɨɪɢɬɦɢɡɢɪɭɟɬɫɹ
2. ɍɬɨɱɧɟɧɢɟ ɩɨɥɨɠɟɧɢɹ ɤɨɪɧɹ ɧɚ ɢɧɬɟɪɜɚɥɟ ɢɡɨɥɹɰɢɢ. ɋɜɨɣɫɬɜɚ ɮɭɧɤɰɢɢ ɧɚ ɢɧɬɟɪɜɚɥɟ ɢɡɨɥɹɰɢɢ [a, b]:
2.1.f (x) ɧɟɩɪɟɪɵɜɧɚ ɧɚ >a, b];
2.2.f (x) ɦɨɧɨɬɨɧɧɚ ɧɚ >a, b@ ɬ ɟ f c(x) ! 0 ɢɥɢ f c(x) 0 ɱɬɨ
ɨɛɭɫɥɚɜɥɢɜɚɟɬ ɟɞɢɧɫɬɜɟɧɧɨɫɬɶ ɤɨɪɧɹ;
2.3. f (x) ɦɟɧɹɟɬ ɡɧɚɤ ɧɚ >a, b], f (a) f (b) 0 ɬ ɟ ɤɨɪɟɧɶ ɫɭɳɟ
ɫɬɜɭɟɬ;
2.4. f (x) ɧɟ ɢɦɟɟɬ ɬɨɱɟɤ ɩɟɪɟɝɢɛɚ ɬ ɟ f cc(x) ! 0 ɢɥɢ f cc(x) 0. ɉɨɫɥɟɞɧɢɟ ɭɫɥɨɜɢɹ ɧɟ ɹɜɥɹɸɬɫɹ ɜ ɨɛɳɟɦ ɫɥɭɱɚɟ ɨɛɹɡɚɬɟɥɶɧɵ
ɦɢ ɧɨ ɞɥɹ ɫɯɨɞɢɦɨɫɬɢ ɧɟɤɨɬɨɪɵɯ ɦɟɬɨɞɨɜ ɨɧɢ ɧɟɨɛɯɨɞɢɦɵ Ɍɚɤ ɟɫɥɢ ɮɭɧɤɰɢɹ ɢɦɟɟɬ ɤɨɪɟɧɶ ɜ ɬɨɱɤɟ ɫɜɨɟɝɨ ɥɨɤɚɥɶɧɨɝɨ ɦɢɧɢɦɭɦɚ ɭɫɥɨɜɢɟ ɧɟ ɜɵɩɨɥɧɹɟɬɫɹ ɨɞɧɚɤɨ ɨɧɨ ɧɟɨɛɯɨɞɢɦɨ ɞɥɹ ɫɯɨɞɢ ɦɨɫɬɢ ɦɟɬɨɞɨɜ ɞɢɯɨɬɨɦɢɢ ɯɨɪɞ ɢ ɫɟɤɭɳɢɯ Ⱦɥɹ ɫɯɨɞɢɦɨɫɬɢ ɦɟɬɨ ɞɚ ɫɟɤɭɳɢɯ ɬɚɤɠɟ ɧɟɨɛɯɨɞɢɦɨ ɜɵɩɨɥɧɟɧɢɟ ɭɫɥɨɜɢɹ
ɇɚɯɨɠɞɟɧɢɟ ɩɪɢɛɥɢɠɟɧɧɨɝɨ ɡɧɚɱɟɧɢɹ ɤɨɪɧɹ – ɷɬɨ ɢɬɟɪɚɰɢɨɧ ɧɵɣ ɩɪɨɰɟɫɫ ɤɨɝɞɚ ɩɨ ɩɪɟɞɵɞɭɳɟɦɭ ɩɪɟɞɵɞɭɳɢɦ ɡɧɚɱɟɧɢɹɦ ɤɨɪɧɹ ɧɚɯɨɞɢɬɫɹ ɫɥɟɞɭɸɳɟɟ ɩɪɢɛɥɢɠɟɧɧɨɟ ɡɧɚɱɟɧɢɟ ɂɬɟɪɚɰɢɨɧ ɧɵɣ ɩɪɨɰɟɫɫ ɩɪɟɤɪɚɳɚɟɬɫɹ ɤɨɝɞɚ ɞɨɫɬɢɝɚɟɬɫɹ ɡɚɞɚɧɧɚɹ ɬɨɱɧɨɫɬɶ
f (xn H) f (xn H) 0 . |
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18
Ⱦɥɹ ɷɬɨɝɨ ɧɟɨɛɯɨɞɢɦɨ ɱɬɨɛɵ ɩɪɨɰɟɫɫ ɢɬɟɪɚɰɢɣ ɫɯɨɞɢɥɫɹ Ɋɚɫ ɫɦɨɬɪɢɦ ɧɟɫɤɨɥɶɤɨ ɢɬɟɪɚɰɢɨɧɧɵɯ ɩɪɨɰɟɞɭɪ
Ɇɟɬɨɞ ɩɪɨɫɬɨɣ ɢɬɟɪɚɰɢɢ ɞɥɹ ɪɟɲɟɧɢɹ ɧɟɥɢɧɟɣɧɵɯ ɢ ɬɪɚɧɫɰɟɧɞɟɧɬɧɵɯ ɭɪɚɜɧɟɧɢɣ
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ɍɪɚɜɧɟɧɢɟ f (x) |
0 ɩɪɟɨɛɪɚɡɭɟɬɫɹ ɤ ɜɢɞɭ |
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(3.1.1) |
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ɢ ɟɫɥɢ ɜɵɩɨɥɧɹɟɬɫɹ ɭɫɥɨɜɢɟ |
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c |
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1, |
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(3.1.2) |
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I |
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ɬɨ ɢɬɟɪɚɰɢɨɧɧɵɣ ɩɪɨɰɟɫɫ |
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(3.1.3) |
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xk 1 I(xk ) |
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ɫɯɨɞɢɬɫɹ |
ɤ |
ɬɨɱɧɨɦɭ |
ɡɧɚɱɟɧɢɸ |
Ⱦɟɣɫɬɜɢɬɟɥɶɧɨ |
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xk 1 xk |
I(xk ) I(xk 1) ɢɡ ɬɟɨɪɟɦɵ ɨ ɫɪɟɞɧɟɦ ɫɥɟɞɭɟɬ ɨɰɟɧɤɚ |
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xk 1 xk |
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d M1 |
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xk xk 1 |
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ɬ ɟ ɪɚɫɫɬɨɹɧɢɟ ɦɟɠɞɭ ɬɨɱɤɚɦɢ ɩɨɫɥɟ |
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ɞɨɜɚɬɟɥɶɧɨɫɬɢ ɭɦɟɧɶɲɚɟɬɫɹ ɟɫɥɢ M1 1 — ( M1 max Ic = q –
ɡɧɚɦɟɧɚɬɟɥɶ ɫɯɨɞɢɦɨɫɬɢ ɉɨ ɬɟɨɪɟɦɟ ɨ ɧɟɩɨɞɜɢɠɧɨɣ ɬɨɱɤɟ ɜ ɷɬɨɦ ɫɥɭɱɚɟ ɫɭɳɟɫɬɜɭɟɬ ɩɪɟɞɟɥ — ɪɟɲɟɧɢɟ ɭɪɚɜɧɟɧɢɹ ɇɚɱɚɥɶɧɚɹ ɬɨɱɤɚ x0 — ɥɸɛɚɹ ɬɨɱɤɚ ɢɧɬɟɪɜɚɥɚ ɥɨɤɚɥɢɡɚɰɢɢ ɤɨɪɧɹ Ɂɧɚɦɟɧɚ
ɬɟɥɶ ɫɯɨɞɢɦɨɫɬɢ ɡɚɜɢɫɢɬ ɨɬ ɜɢɞɚ I(x) ɍɪɚɜɧɟɧɢɟ f (x) 0 ɦɨɠɟɬ ɛɵɬɶ ɩɪɟɨɛɪɚɡɨɜɚɧɨ ɤ ɢɬɟɪɚɰɢɨɧɧɨɦɭ ɜɢɞɭ ɦɧɨɠɟɫɬɜɨɦ ɪɚɡɥɢɱɧɵɯ ɫɩɨɫɨɛɨɜ – ɦɨɞɢɮɢɤɚɰɢɣ ɨɞɧɨɲɚɝɨɜɨɝɨ ɫɬɚɰɢɨɧɚɪɧɨ ɝɨ ɦɟɬɨɞɚ ɩɪɨɫɬɨɣ ɢɬɟɪɚɰɢɢ ɫɦ ɬɚɤɠɟ ɜɵɛɨɪɨɦ ɤɨɬɨɪɵɯ ɦɨɠɧɨ ɞɨɛɢɬɶɫɹ ɦɢɧɢɦɭɦɚ ɡɧɚɦɟɧɚɬɟɥɹ ɫɯɨɞɢɦɨɫɬɢ ɇɚɩɪɢɦɟɪ ɢɫɯɨɞɧɨɟ ɭɪɚɜɧɟɧɢɟ ɷɤɜɢɜɚɥɟɧɬɧɨ ɫɥɟɞɭɸɳɟɦɭ
x x Of (x) Ⱦɨɫɬɚɬɨɱɧɨɟ ɭɫɥɨɜɢɟ ɫɯɨɞɢɦɨɫɬɢ ɜɵɩɨɥɧɹ
ɟɬɫɹ ɟɫɥɢ O |
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, f (x) ! 0, ɝɞɟ M1 |
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M1 |
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Ɇɟɬɨɞ ɯɨɪɞ ɢ ɫɟɤɭɳɢɯ |
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ɇɚ ɢɧɬɟɪɜɚɥɟ [a,b] |
ɡɚɦɟɧɢɦ f (x) |
ɥɢɧɟɣɧɵɦ ɢɧɬɟɪɩɨɥɹɰɢɨɧ |
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ɧɵɦ ɩɨɥɢɧɨɦɨɦ ɩɪɨɯɨɞɹɳɟɦ ɱɟɪɟɡ ɬɨɱɤɢ (a, f (a) ɢ (b, f (b)) : |
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P (x) |
f (a) |
f (b) f (a) |
(x a) . |
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19
ȼ ɤɚɱɟɫɬɜɟ ɩɟɪɜɨɝɨ ɩɪɢɛɥɢɠɟɧɧɨɝɨ ɡɧɚɱɟɧɢɹ ɤɨɪɧɹ ɜɵɛɟɪɟɦ
ɤɨɪɟɧɶ ɩɨɥɢɧɨɦɚ P1(x) 0 ɬɨɝɞɚ
x a |
f (a)(b a) |
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(3.2.1) |
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f (b) f (a) |
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Ⱦɚɥɟɟ ɟɫɥɢ ɩɨɜɟɞɟɧɢɟ f cc(x) ɧɟɢɡɜɟɫɬɧɨ ɬɨ ɜɵɛɢɪɚɸɬ ɢɧɬɟɪɜɚɥ
ɧɚ ɤɨɬɨɪɨɦ f (x) ɦɟɧɹɟɬ ɡɧɚɤ [a; x1] ɢɥɢ [x1, a] ɢ ɧɚ ɧɟɦ ɫɬɪɨɹɬ ɧɨɜɭɸ ɯɨɪɞɭ ɬ ɟ ɜ ɮɨɪɦɭɥɭ ɩɨɞɫɬɚɜɥɹɟɦ ɧɨɜɵɟ ɝɪɚɧɢɰɵ ɢɧɬɟɪ ɜɚɥɚ ɢ ɬ ɞ ɞɨ ɞɨɫɬɢɠɟɧɢɹ ɡɚɞɚɧɧɨɣ ɬɨɱɧɨɫɬɢ
ȿɫɥɢ f (x) |
ɧɟ ɢɦɟɟɬ ɬɨɱɤɢ ɩɟɪɟɝɢɛɚ ɧɚ [a;b] ɬɨ ɨɞɢɧ ɢɡ ɤɨɧɰɨɜ |
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ɦɧɨɠɟɫɬɜɚ ɯɨɪɞ ɧɟɩɨɞɜɢɠɟɧ ɍɫɥɨɜɢɟ ɧɟɩɨɞɜɢɠɧɨɣ ɬɨɱɤɢ |
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a,ɟɫɥɢf a f |
cc |
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a ² |
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(3.2.2) |
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¯b,ɟɫɥɢf b f |
b ² |
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Ⱥɧɚɥɢɡ f |
(x) ɩɨɡɜɨɥɹɟɬ ɨɩɪɟɞɟɥɢɬɶ ɧɟɩɨɞɜɢɠɧɭɸ ɬɨɱɤɭ c ɢ ɞɥɹ |
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ɧɚɯɨɠɞɟɧɢɹ xn 1 ɢɫɩɨɥɶɡɨɜɚɬɶ ɢɬɟɪɚɰɢɨɧɧɭɸ ɮɨɪɦɭɥɭ |
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xn 1 |
I(xn ) |
xn |
f (xn ) |
c xn , |
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f (c) f (xn ) |
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ɩɪɢɱɟɦ x0 c .
ɉɪɢ ɨɬɫɭɬɫɬɜɢɢ ɬɨɱɤɢ ɩɟɪɟɝɢɛɚ ɜ ɨɛɥɚɫɬɢ ɥɨɤɚɥɢɡɚɰɢɢ ɤɨɪɧɹ ɛɨɥɟɟ ɷɮɮɟɤɬɢɜɧɵɦ ɹɜɥɹɟɬɫɹ ɞɜɭɯɲɚɝɨɜɵɣ ɦɟɬɨɞ ɫɟɤɭɳɢɯ ɜ ɤɨ ɬɨɪɨɦ ɩɨɫɥɟɞɭɸɳɟɟ ɩɪɢɛɥɢɠɟɧɧɨɟ ɡɧɚɱɟɧɢɟ ɤɨɪɧɹ ɧɚɯɨɞɢɬɫɹ ɩɨ ɞɜɭɦ ɩɪɟɞɵɞɭɳɢɦ ɑɟɪɟɡ ɩɟɪɜɵɟ ɞɜɟ ɬɨɱɤɢ ɩɪɨɜɨɞɢɬɫɹ ɫɟɤɭɳɚɹ ɩɟɪɟɫɟɱɟɧɢɟ ɤɨɬɨɪɨɣ ɫ ɨɫɶɸ ɚɛɫɰɢɫɫ ɞɚɟɬ ɫɥɟɞɭɸɳɟɟ ɩɪɢɛɥɢɠɟɧ ɧɨɟ ɡɧɚɱɟɧɢɟ ȼ ɪɟɡɭɥɶɬɚɬɟ ɩɪɢɯɨɞɢɦ ɤ ɢɬɟɪɚɰɢɨɧɧɨɣ ɮɨɪɦɭɥɟ
xn 1 xn |
f (xn ) |
xn xn 1 |
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Ⱥɧɚɥɨɝɢɱɧɚɹ ɮɨɪɦɭɥɚ ɩɨɥɭɱɚɟɬɫɹ ɟɫɥɢ ɜ ɩɪɚɜɨɣ ɱɚɫɬɢ ɮɨɪɦɭɥɵ ɦɟɬɨɞɚ ɇɶɸɬɨɧɚ ɜɦɟɫɬɨ ɩɪɨɢɡɜɨɞɧɨɣ ɨɬ ɮɭɧɤɰɢɢ ɩɨɞɫɬɚɜɢɬɶ ɟɺ ɤɨɧɟɱɧɨɪɚɡɧɨɫɬɧɭɸ ɚɩɩɪɨɤɫɢɦɚɰɢɸ ɩɟɪɜɨɝɨ ɩɨɪɹɞɤɚ ɜ ɬɨɱɤɟ xn .
20
Ɇɟɬɨɞ ɤɚɫɚɬɟɥɶɧɵɯ (ɦɟɬɨɞ ɇɶɸɬɨɧɚ
ȼ ɷɬɨɦ ɦɟɬɨɞɟ ɜ ɤɚɱɟɫɬɜɟ x0 ɜɵɛɢɪɚɟɬɫɹ ɨɞɧɚ ɢɡ ɝɪɚɧɢɰ ɢɧɬɟɪ ɜɚɥɚ [a,b] ɢ ɢɡ ɷɬɨɣ ɬɨɱɤɢ ɫɬɪɨɢɬɫɹ ɤɚɫɚɬɟɥɶɧɚɹ ȼ ɤɚɱɟɫɬɜɟ ɩɪɢ ɛɥɢɠɟɧɧɨɝɨ ɡɧɚɱɟɧɢɹ ɤɨɪɧɹ x1 ɩɪɢɧɢɦɚɟɬɫɹ ɬɨɱɤɚ ɩɟɪɟɫɟɱɟɧɢɹ ɤɚɫɚɬɟɥɶɧɨɣ ɫ ɨɫɶɸ ɚɛɫɰɢɫɫ ɂɡ ɬɨɱɤɢ (x1, f (x1) ɩɪɨɜɨɞɢɬɫɹ ɧɨɜɚɹ
ɤɚɫɚɬɟɥɶɧɚɹ ɢ ɬ ɞ ɞɨ ɞɨɫɬɢɠɟɧɢɹ ɡɚɞɚɧɧɨɣ ɬɨɱɧɨɫɬɢ ɍɪɚɜɧɟɧɢɟ ɤɚɫɚɬɟɥɶɧɨɣ ɜ ɬɨɱɤɟ xn ɢɦɟɟɬ ɜɢɞ
yk (x) f (xn ) f c(xn ) (x xn ) , yk (xn 1) 0 ,
ɨɬɫɸɞɚ ɫɥɟɞɭɟɬ ɢɬɟɪɚɰɢɨɧɧɵɣ ɩɪɨɰɟɫɫ
xn 1 I(xn ) xn |
f (xn ) |
f c(xn ) |
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(3.3.1) |
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ȼɵɪɚɠɟɧɢɟ ɞɥɹ ɧɚɱɚɥɶɧɨɣ ɬɨɱɤɢ x0 ɫɨɜɩɚɞɚɟɬ ɫ
Ɇɟɬɨɞ ɇɶɸɬɨɧɚ ɦɨɠɧɨ ɫɱɢɬɚɬɶ ɦɨɞɢɮɢɤɚɰɢɟɣ ɦɟɬɨɞɚ ɩɪɨɫɬɨɣ ɢɬɟɪɚɰɢɢ ɩɪɢ I(x) x f (x)
f c(x) ɍɫɥɨɜɢɹ ɫɯɨɞɢɦɨɫɬɢ ɦɟɬɨɞɚ ɫɥɟɞɭɸɬ ɢɡ ɚ ɢɦɟɧɧɨ ɞɥɹ ɜɫɟɯ x ɢɡ ɨɛɥɚɫɬɢ ɥɨɤɚ ɥɢɡɚɰɢɢ ɤɨɪɧɹ ɞɨɥɠɧɨ ɜɵɩɨɥɧɹɬɶɫɹ
q |
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< 1. |
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ɂɡ ɫɥɟɞɭɟɬ ɱɬɨ ɱɟɦ ɦɟɧɶɲɟ ɨɛɥɚɫɬɶ ɥɨɤɚɥɢɡɚɰɢɢ ɤɨɪɧɹ ɬɟɦ ɦɟɧɶɲɟ ɡɧɚɦɟɧɚɬɟɥɶ q ɫɯɨɞɢɦɨɫɬɢ ɦɟɬɨɞɚ ɇɶɸɬɨɧɚ ɢ ɜ ɩɪɟɞɟɥɟ
q o 0 ɩɪɢ x o x Ɍɚɤɢɦ ɨɛɪɚɡɨɦ ɩɪɢ ɞɨɫɬɚɬɨɱɧɨ ɦɚɥɨɣ ɨɛɥɚɫɬɢ ɥɨɤɚɥɢɡɚɰɢɢ ɤɨɪɧɹ ɫɯɨɞɢɦɨɫɬɶ ɦɟɬɨɞɚ ɇɶɸɬɨɧɚ ɛɟɡɭɫɥɨɜɧɚɹ
3.4. ɋɤɨɪɨɫɬɶ ɫɯɨɞɢɦɨɫɬɢ ɢɬɟɪɚɰɢɨɧɧɵɯ ɦɟɬɨɞɨɜ
ȼɜɟɞɟɦ ɨɛɨɡɧɚɱɟɧɢɹ 'x x x*, 'x x x Ⱦɥɹ ɨɰɟɧɤɢ
n n n n n 1
ɫɤɨɪɨɫɬɢ ɫɯɨɞɢɦɨɫɬɢ ɧɟɨɛɯɨɞɢɦɨ ɨɩɪɟɞɟɥɢɬɶ ɡɚɜɢɫɢɦɨɫɬɶ ɦɟɠɞɭ
'x |
ɢ 'x . |
n 1 |
n |
ȿɫɥɢ ɜ ɩɪɨɰɟɫɫɟ ɢɬɟɪɚɰɢɣ ɧɚɱɢɧɚɹ ɫ ɧɟɤɨɬɨɪɨɝɨ n ɜɵɩɨɥɧɹɟɬɫɹ
'x
n 1 d q ɝɞɟ r, q const , (3.4.1)
'xn r
