85 lines
2.7 KiB
Fortran
85 lines
2.7 KiB
Fortran
recursive function evapol(tu,nu,tv,nv,c,rad,x,y) result(e_res)
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implicit none
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real*8 :: e_res
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c function program evacir evaluates the function f(x,y) = s(u,v),
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c defined through the transformation
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c x = u*rad(v)*cos(v) y = u*rad(v)*sin(v)
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c and where s(u,v) is a bicubic spline ( 0<=u<=1 , -pi<=v<=pi ), given
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c in its standard b-spline representation.
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c
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c calling sequence:
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c f = evapol(tu,nu,tv,nv,c,rad,x,y)
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c
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c input parameters:
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c tu : real array, length nu, which contains the position of the
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c knots in the u-direction.
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c nu : integer, giving the total number of knots in the u-direction
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c tv : real array, length nv, which contains the position of the
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c knots in the v-direction.
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c nv : integer, giving the total number of knots in the v-direction
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c c : real array, length (nu-4)*(nv-4), which contains the
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c b-spline coefficients.
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c rad : real function subprogram, defining the boundary of the
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c approximation domain. must be declared external in the
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c calling (sub)-program
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c x,y : real values.
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c before entry x and y must be set to the co-ordinates of
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c the point where f(x,y) must be evaluated.
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c
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c output parameter:
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c f : real
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c on exit f contains the value of f(x,y)
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c
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c other subroutines required:
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c bispev,fpbisp,fpbspl
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c
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c references :
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c de boor c : on calculating with b-splines, j. approximation theory
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c 6 (1972) 50-62.
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c cox m.g. : the numerical evaluation of b-splines, j. inst. maths
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c applics 10 (1972) 134-149.
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c dierckx p. : curve and surface fitting with splines, monographs on
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c numerical analysis, oxford university press, 1993.
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c
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c author :
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c p.dierckx
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c dept. computer science, k.u.leuven
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c celestijnenlaan 200a, b-3001 heverlee, belgium.
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c e-mail : Paul.Dierckx@cs.kuleuven.ac.be
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c
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c latest update : march 1989
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c
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c ..scalar arguments..
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integer nu,nv
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real*8 x,y
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c ..array arguments..
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real*8 tu(nu),tv(nv),c((nu-4)*(nv-4))
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c ..user specified function
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real*8 rad
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c ..local scalars..
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integer ier
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real*8 u,v,r,f,one,dist
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c ..local arrays
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real*8 wrk(8)
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integer iwrk(2)
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c ..function references
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real*8 atan2,sqrt
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c ..
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c calculate the (u,v)-coordinates of the given point.
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one = 1
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u = 0.
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v = 0.
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dist = x**2+y**2
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if(dist.le.0.) go to 10
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v = atan2(y,x)
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r = rad(v)
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if(r.le.0.) go to 10
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u = sqrt(dist)/r
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if(u.gt.one) u = one
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c evaluate s(u,v)
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10 call bispev(tu,nu,tv,nv,c,3,3,u,1,v,1,f,wrk,8,iwrk,2,ier)
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e_res = f
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return
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end
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