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module coefpoly_m |
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IMPLICIT NONE |
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contains |
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SUBROUTINE coefpoly(xf1, xf2, xprim1, xprim2, xtild1, xtild2, a0, a1, a2, a3) |
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! From LMDZ4/libf/dyn3d/coefpoly.F, version 1.1.1.1 2004/05/19 12:53:05 |
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! Author: P. Le Van |
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! Calcul des coefficients a0, a1, a2, a3 du polynôme de degré 3 qui |
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! satisfait aux 4 équations suivantes : |
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! a0 + a1 * xtild1 + a2 * xtild1**2 + a3 * xtild1**3 = Xf1 |
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! a0 + a1 * xtild2 + a2 * xtild2**2 + a3 * xtild2**3 = Xf2 |
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! a1 + 2. * a2 * xtild1 + 3. * a3 * xtild1**2 = Xprim1 |
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! a1 + 2. * a2 * xtild2 + 3. * a3 * xtild2**2 = Xprim2 |
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! (passe par les points (Xf(it), xtild(it)) et (Xf(it + 1), |
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! xtild(it + 1)) |
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! On en revient à resoudre un système de 4 équations à 4 inconnues |
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! a0, a1, a2, a3. |
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use nrtype, only: k8 |
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REAL(K8), intent(in):: xf1, xf2, xprim1, xprim2, xtild1, xtild2 |
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REAL(K8), intent(out):: a0, a1, a2, a3 |
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! Local: |
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REAL(K8) xtil1car, xtil2car, derr, x1x2car |
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!------------------------------------------------------------ |
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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 |
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end module coefpoly_m |
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