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Last change
on this file since 1834 was
135,
checked in by aslmd, 14 years ago
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CHANGEMENT ARBORESCENCE ETAPE 2 -- NON COMPLET
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File size:
894 bytes
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| 1 | subroutine lagrange(x, xi, yi, ans) |
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| 2 | |
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| 3 | C Lagrange interpolation - Polynomial interpolation at point x |
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| 4 | C xi(1) <= x <= xi(4). Yi(n) is the functional value at XI(n). |
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| 5 | |
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| 6 | implicit none |
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| 7 | |
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| 8 | real*8 x, xi(4), yi(4), ans |
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| 9 | real*8 fm1, fm2, fm3, fm4 |
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| 10 | |
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| 11 | C======================================================================! |
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| 12 | |
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| 13 | fm1 = x - XI(1) |
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| 14 | fm2 = x - XI(2) |
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| 15 | fm3 = x - XI(3) |
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| 16 | fm4 = x - XI(4) |
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| 17 | |
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| 18 | C Get the answer at the requested X |
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| 19 | |
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| 20 | ans = fm2*fm3*fm4*YI(1)/ |
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| 21 | * ((XI(1)-XI(2))*(XI(1)-XI(3))*(XI(1)-XI(4))) + |
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| 22 | * fm1*fm3*fm4*YI(2)/ |
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| 23 | * ((XI(2)-XI(1))*(XI(2)-XI(3))*(XI(2)-XI(4))) + |
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| 24 | * fm1*fm2*fm4*YI(3)/ |
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| 25 | * ((XI(3)-XI(1))*(XI(3)-XI(2))*(XI(3)-XI(4))) + |
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| 26 | * fm1*fm2*fm3*YI(4)/ |
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| 27 | * ((XI(4)-XI(1))*(XI(4)-XI(2))*(XI(4)-XI(3))) |
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| 28 | |
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| 29 | return |
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| 30 | end |
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