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subroutine fpcurf(iopt,x,y,w,m,xb,xe,k,s,nest,tol,maxit,k1,k2,
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* n,t,c,fp,fpint,z,a,b,g,q,nrdata,ier)
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integer iopt,m,k,nest,maxit,k1,k2,n,ier
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real*8 x(m),y(m),w(m),t(nest),c(nest),fpint(nest),
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* z(nest),a(nest,k1),b(nest,k2),g(nest,k2),q(m,k1)
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real*8 acc,con1,con4,con9,cos,half,fpart,fpms,fpold,fp0,f1,f2,f3,
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* one,p,pinv,piv,p1,p2,p3,rn,sin,store,term,wi,xi,yi
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integer i,ich1,ich3,it,iter,i1,i2,i3,j,k3,l,l0,
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* mk1,new,nk1,nmax,nmin,nplus,npl1,nrint,n8
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c ..function references
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c ..subroutine references..
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c fpback,fpbspl,fpgivs,fpdisc,fpknot,fprota
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cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
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c part 1: determination of the number of knots and their position c
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c ************************************************************** c
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c given a set of knots we compute the least-squares spline sinf(x), c
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c and the corresponding sum of squared residuals fp=f(p=inf). c
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c if iopt=-1 sinf(x) is the requested approximation. c
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c if iopt=0 or iopt=1 we check whether we can accept the knots: c
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c if fp <=s we will continue with the current set of knots. c
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c if fp > s we will increase the number of knots and compute the c
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c corresponding least-squares spline until finally fp<=s. c
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c the initial choice of knots depends on the value of s and iopt. c
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c if s=0 we have spline interpolation; in that case the number of c
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c knots equals nmax = m+k+1. c
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c iopt=0 we first compute the least-squares polynomial of c
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c degree k; n = nmin = 2*k+2 c
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c iopt=1 we start with the set of knots found at the last c
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c call of the routine, except for the case that s > fp0; then c
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c we compute directly the least-squares polynomial of degree k. c
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cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
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c determine nmin, the number of knots for polynomial approximation.
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if(iopt.lt.0) go to 60
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c calculation of acc, the absolute tolerance for the root of f(p)=s.
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c determine nmax, the number of knots for spline interpolation.
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if(s.gt.0.0d0) go to 45
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c if s=0, s(x) is an interpolating spline.
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c test whether the required storage space exceeds the available one.
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if(nmax.gt.nest) go to 420
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c find the position of the interior knots in case of interpolation.
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if(k3*2.eq.k) go to 30
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t(i) = (x(j)+x(j-1))*half
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c if s>0 our initial choice of knots depends on the value of iopt.
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c if iopt=0 or iopt=1 and s>=fp0, we start computing the least-squares
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c polynomial of degree k which is a spline without interior knots.
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c if iopt=1 and fp0>s we start computing the least squares spline
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c according to the set of knots found at the last call of the routine.
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45 if(iopt.eq.0) go to 50
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if(n.eq.nmin) go to 50
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c main loop for the different sets of knots. m is a save upper bound
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c for the number of trials.
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if(n.eq.nmin) ier = -2
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c find nrint, tne number of knot intervals.
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c find the position of the additional knots which are needed for
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c the b-spline representation of s(x).
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c compute the b-spline coefficients of the least-squares spline
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c sinf(x). the observation matrix a is built up row by row and
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c reduced to upper triangular form by givens transformations.
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c at the same time fp=f(p=inf) is computed.
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c initialize the observation matrix a.
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c fetch the current data point x(it),y(it).
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c search for knot interval t(l) <= xi < t(l+1).
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85 if(xi.lt.t(l+1) .or. l.eq.nk1) go to 90
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c evaluate the (k+1) non-zero b-splines at xi and store them in q.
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90 call fpbspl(t,n,k,xi,l,h)
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c rotate the new row of the observation matrix into triangle.
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if(piv.eq.0.0d0) go to 110
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c calculate the parameters of the givens transformation.
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call fpgivs(piv,a(j,1),cos,sin)
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c transformations to right hand side.
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call fprota(cos,sin,yi,z(j))
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if(i.eq.k1) go to 120
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c transformations to left hand side.
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call fprota(cos,sin,h(i1),a(j,i2))
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c add contribution of this row to the sum of squares of residual
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if(ier.eq.(-2)) fp0 = fp
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c backward substitution to obtain the b-spline coefficients.
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call fpback(a,z,nk1,k1,c,nest)
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c test whether the approximation sinf(x) is an acceptable solution.
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if(iopt.lt.0) go to 440
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if(abs(fpms).lt.acc) go to 440
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c if f(p=inf) < s accept the choice of knots.
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if(fpms.lt.0.0d0) go to 250
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c if n = nmax, sinf(x) is an interpolating spline.
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if(n.eq.nmax) go to 430
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c increase the number of knots.
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c if n=nest we cannot increase the number of knots because of
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c the storage capacity limitation.
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if(n.eq.nest) go to 420
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c determine the number of knots nplus we are going to add.
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if(ier.eq.0) go to 140
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if(fpold-fp.gt.acc) npl1 = rn*fpms/(fpold-fp)
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nplus = min0(nplus*2,max0(npl1,nplus/2,1))
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c compute the sum((w(i)*(y(i)-s(x(i))))**2) for each knot interval
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c t(j+k) <= x(i) <= t(j+k+1) and store it in fpint(j),j=1,2,...nrint.
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if(x(it).lt.t(l) .or. l.gt.nk1) go to 160
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term = term+c(l0)*q(it,j)
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term = (w(it)*(term-y(it)))**2
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if(new.eq.0) go to 180
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fpint(i) = fpart-store
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call fpknot(x,m,t,n,fpint,nrdata,nrint,nest,1)
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c if n=nmax we locate the knots as for interpolation.
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if(n.eq.nmax) go to 10
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c test whether we cannot further increase the number of knots.
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if(n.eq.nest) go to 200
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c restart the computations with the new set of knots.
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c test whether the least-squares kth degree polynomial is a solution
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c of our approximation problem.
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250 if(ier.eq.(-2)) go to 440
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cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
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c part 2: determination of the smoothing spline sp(x). c
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c *************************************************** c
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c we have determined the number of knots and their position. c
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c we now compute the b-spline coefficients of the smoothing spline c
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c sp(x). the observation matrix a is extended by the rows of matrix c
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c b expressing that the kth derivative discontinuities of sp(x) at c
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c the interior knots t(k+2),...t(n-k-1) must be zero. the corres- c
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c ponding weights of these additional rows are set to 1/p. c
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c iteratively we then have to determine the value of p such that c
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c f(p)=sum((w(i)*(y(i)-sp(x(i))))**2) be = s. we already know that c
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c the least-squares kth degree polynomial corresponds to p=0, and c
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c that the least-squares spline corresponds to p=infinity. the c
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c iteration process which is proposed here, makes use of rational c
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c interpolation. since f(p) is a convex and strictly decreasing c
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c function of p, it can be approximated by a rational function c
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c r(p) = (u*p+v)/(p+w). three values of p(p1,p2,p3) with correspond- c
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c ing values of f(p) (f1=f(p1)-s,f2=f(p2)-s,f3=f(p3)-s) are used c
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c to calculate the new value of p such that r(p)=s. convergence is c
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c guaranteed by taking f1>0 and f3<0. c
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cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
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c evaluate the discontinuity jump of the kth derivative of the
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c b-splines at the knots t(l),l=k+2,...n-k-1 and store in b.
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call fpdisc(t,n,k2,b,nest)
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c initial value for p.
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c iteration process to find the root of f(p) = s.
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c the rows of matrix b with weight 1/p are rotated into the
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c triangularised observation matrix a which is stored in g.
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c the row of matrix b is rotated into triangle by givens transformation
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c calculate the parameters of the givens transformation.
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call fpgivs(piv,g(j,1),cos,sin)
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c transformations to right hand side.
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call fprota(cos,sin,yi,c(j))
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if(j.eq.nk1) go to 300
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if(j.gt.n8) i2 = nk1-j
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c transformations to left hand side.
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call fprota(cos,sin,h(i1),g(j,i1))
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c backward substitution to obtain the b-spline coefficients.
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call fpback(g,c,nk1,k2,c,nest)
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c computation of f(p).
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if(x(it).lt.t(l) .or. l.gt.nk1) go to 310
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term = term+c(l0)*q(it,j)
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fp = fp+(w(it)*(term-y(it)))**2
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c test whether the approximation sp(x) is an acceptable solution.
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if(abs(fpms).lt.acc) go to 440
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c test whether the maximal number of iterations is reached.
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if(iter.eq.maxit) go to 400
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c carry out one more step of the iteration process.
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if(ich3.ne.0) go to 340
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if((f2-f3).gt.acc) go to 335
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c our initial choice of p is too large.
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if(p.le.p1) p=p1*con9 + p2*con1
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335 if(f2.lt.0.0d0) ich3=1
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340 if(ich1.ne.0) go to 350
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if((f1-f2).gt.acc) go to 345
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c our initial choice of p is too small
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if(p3.lt.0.) go to 360
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if(p.ge.p3) p = p2*con1 + p3*con9
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345 if(f2.gt.0.0d0) ich1=1
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c test whether the iteration process proceeds as theoretically
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350 if(f2.ge.f1 .or. f2.le.f3) go to 410
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c find the new value for p.
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p = fprati(p1,f1,p2,f2,p3,f3)
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c error codes and messages.
added
removed
Lib/interpolate/fitpack/fpcurf.f
