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! $Header: /home/cvsroot/LMDZ4/libf/dyn3d/coefpoly.F,v 1.1.1.1 2004/05/19 |
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! 12:53:05 lmdzadmin Exp $ |
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SUBROUTINE coefpoly(xf1, xf2, xprim1, xprim2, xtild1, xtild2, a0, a1, a2, a3) |
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IMPLICIT NONE |
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! ... Auteur : P. Le Van ... |
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! Calcul des coefficients a0, a1, a2, a3 du polynome de degre 3 qui |
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! satisfait aux 4 equations suivantes : |
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! a0 + a1*xtild1 + a2*xtild1*xtild1 + a3*xtild1*xtild1*xtild1 = Xf1 |
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! a0 + a1*xtild2 + a2*xtild2*xtild2 + a3*xtild2*xtild2*xtild2 = Xf2 |
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! a1 + 2.*a2*xtild1 + 3.*a3*xtild1*xtild1 = Xprim1 |
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! a1 + 2.*a2*xtild2 + 3.*a3*xtild2*xtild2 = Xprim2 |
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! On en revient a resoudre un systeme de 4 equat.a 4 inconnues a0,a1,a2,a3 |
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DOUBLE PRECISION xf1, xf2, xprim1, xprim2, xtild1, xtild2 |
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DOUBLE PRECISION a1, a2, a3, a0, xtil1car, xtil2car, derr, x1x2car |
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xtil1car = xtild1*xtild1 |
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xtil2car = xtild2*xtild2 |
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derr = 2.*(xf2-xf1)/(xtild1-xtild2) |
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x1x2car = (xtild1-xtild2)*(xtild1-xtild2) |
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a3 = (derr+xprim1+xprim2)/x1x2car |
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a2 = (xprim1-xprim2+3.*a3*(xtil2car-xtil1car))/(2.*(xtild1-xtild2)) |
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a1 = xprim1 - 3.*a3*xtil1car - 2.*a2*xtild1 |
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a0 = xf1 - a3*xtild1*xtil1car - a2*xtil1car - a1*xtild1 |
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END SUBROUTINE coefpoly |