[1441] | 1 | module coefpoly_m |
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[1] | 2 | |
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[1441] | 3 | IMPLICIT NONE |
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[1] | 4 | |
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[1441] | 5 | contains |
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[1] | 6 | |
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[1441] | 7 | SUBROUTINE coefpoly(xf1, xf2, xprim1, xprim2, xtild1, xtild2, a0, a1, a2, a3) |
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[1] | 8 | |
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[1441] | 9 | ! From LMDZ4/libf/dyn3d/coefpoly.F, version 1.1.1.1 2004/05/19 12:53:05 |
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[1] | 10 | |
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[1441] | 11 | ! Author: P. Le Van |
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[1] | 12 | |
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[1441] | 13 | ! Calcul des coefficients a0, a1, a2, a3 du polynôme de degré 3 qui |
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| 14 | ! satisfait aux 4 équations suivantes : |
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[1] | 15 | |
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[1441] | 16 | ! a0 + a1 * xtild1 + a2 * xtild1**2 + a3 * xtild1**3 = Xf1 |
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| 17 | ! a0 + a1 * xtild2 + a2 * xtild2**2 + a3 * xtild2**3 = Xf2 |
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| 18 | ! a1 + 2. * a2 * xtild1 + 3. * a3 * xtild1**2 = Xprim1 |
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| 19 | ! a1 + 2. * a2 * xtild2 + 3. * a3 * xtild2**2 = Xprim2 |
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[1] | 20 | |
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[1441] | 21 | ! (passe par les points (Xf(it), xtild(it)) et (Xf(it + 1), |
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| 22 | ! xtild(it + 1)) |
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[1] | 23 | |
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[1441] | 24 | ! On en revient à resoudre un système de 4 équations à 4 inconnues |
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| 25 | ! a0, a1, a2, a3. |
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| 26 | |
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| 27 | use nrtype, only: k8 |
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| 28 | |
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| 29 | REAL(K8), intent(in):: xf1, xf2, xprim1, xprim2, xtild1, xtild2 |
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| 30 | REAL(K8), intent(out):: a0, a1, a2, a3 |
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| 31 | |
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| 32 | ! Local: |
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| 33 | REAL(K8) xtil1car, xtil2car, derr, x1x2car |
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| 34 | |
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| 35 | !------------------------------------------------------------ |
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| 36 | |
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| 37 | xtil1car = xtild1 * xtild1 |
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| 38 | xtil2car = xtild2 * xtild2 |
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| 39 | |
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| 40 | derr = 2. * (xf2-xf1)/(xtild1-xtild2) |
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| 41 | |
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| 42 | x1x2car = (xtild1-xtild2) * (xtild1-xtild2) |
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| 43 | |
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| 44 | a3 = (derr+xprim1+xprim2)/x1x2car |
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| 45 | a2 = (xprim1-xprim2+3. * a3 * (xtil2car-xtil1car))/(2. * (xtild1-xtild2)) |
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| 46 | |
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| 47 | a1 = xprim1 - 3. * a3 * xtil1car - 2. * a2 * xtild1 |
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| 48 | a0 = xf1 - a3 * xtild1 * xtil1car - a2 * xtil1car - a1 * xtild1 |
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| 49 | |
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| 50 | END SUBROUTINE coefpoly |
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| 51 | |
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| 52 | end module coefpoly_m |
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