Sources/misc/coefpoly.f

module coefpoly_m

  IMPLICIT NONE

contains

  SUBROUTINE coefpoly(xf1, xf2, xprim1, xprim2, xtild1, xtild2, a0, a1, a2, a3)

    ! From LMDZ4/libf/dyn3d/coefpoly.F, version 1.1.1.1 2004/05/19 12:53:05

    ! Author: P. Le Van

    ! Calcul des coefficients a0, a1, a2, a3 du polynôme de degré 3 qui
    ! satisfait aux 4 équations suivantes :

    ! a0 + a1 * xtild1 + a2 * xtild1**2 + a3 * xtild1**3 = Xf1
    ! a0 + a1 * xtild2 + a2 * xtild2**2 + a3 * xtild2**3 = Xf2
    ! a1 + 2. * a2 * xtild1 + 3. * a3 * xtild1**2 = Xprim1
    ! a1 + 2. * a2 * xtild2 + 3. * a3 * xtild2**2 = Xprim2

    ! (passe par les points (Xf(it), xtild(it)) et (Xf(it + 1),
    ! xtild(it + 1))

    ! On en revient à resoudre un système de 4 équations à 4 inconnues
    ! a0, a1, a2, a3.

    DOUBLE PRECISION, intent(in):: xf1, xf2, xprim1, xprim2, xtild1, xtild2
    DOUBLE PRECISION, intent(out):: a0, a1, a2, a3

    ! Local:
    DOUBLE PRECISION xtil1car, xtil2car, derr, x1x2car

    !------------------------------------------------------------

    xtil1car = xtild1 * xtild1
    xtil2car = xtild2 * xtild2

    derr = 2. * (xf2-xf1)/(xtild1-xtild2)

    x1x2car = (xtild1-xtild2) * (xtild1-xtild2)

    a3 = (derr+xprim1+xprim2)/x1x2car
    a2 = (xprim1-xprim2+3. * a3 * (xtil2car-xtil1car))/(2. * (xtild1-xtild2))

    a1 = xprim1 - 3. * a3 * xtil1car - 2. * a2 * xtild1
    a0 = xf1 - a3 * xtild1 * xtil1car - a2 * xtil1car - a1 * xtild1

  END SUBROUTINE coefpoly

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