Last change
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checked in by lmdz, 25 years ago
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Initial revision
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Property svn:keywords set to
Author Date Id Revision
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File size:
1.6 KB
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[2] | 1 | subroutine spline(x,y,n,yp1,ypn,y2) |
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| 2 | |
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| 3 | c |
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| 4 | |
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| 5 | c Routine to set up the interpolating function for a cubic spline |
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| 6 | |
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| 7 | c interpolation (see "Numerical Recipes" for details). |
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| 8 | |
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| 9 | c |
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| 10 | implicit real (a-h,o-z) |
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| 11 | implicit integer (i-n) |
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| 12 | |
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| 13 | parameter(nllm=4096) |
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| 14 | |
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| 15 | dimension x(n),y(n),y2(n),u(nllm) |
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| 16 | |
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| 17 | c |
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| 18 | c write(6,*)(x(i),i=1,n) |
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| 19 | c write(6,*)(y(i),i=1,n) |
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| 20 | |
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| 21 | if(yp1.gt.0.99E30) then |
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| 22 | c the lower boundary condition is set |
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| 23 | y2(1)=0. |
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| 24 | c either to be "natural" |
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| 25 | u(1)=0. |
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| 26 | |
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| 27 | else |
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| 28 | c or else to have a specified first |
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| 29 | y2(1)=-0.5 |
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| 30 | c derivative |
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| 31 | u(1)=(3./(x(2)-x(1)))*((y(2)-y(1))/(x(2)-x(1))-yp1) |
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| 32 | |
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| 33 | end if |
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| 34 | |
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| 35 | do 11 i=2,n-1 |
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| 36 | c decomposition loop of the tridiagonal |
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| 37 | sig=(x(i)-x(i-1))/(x(i+1)-x(i-1)) |
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| 38 | c algorithm. Y2 and U are used |
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| 39 | p=sig*y2(i-1)+2. |
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| 40 | c for temporary storage of the decompo- |
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| 41 | y2(i)=(sig-1.)/p |
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| 42 | c sed factors |
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| 43 | u(i)=(6.*((y(i+1)-y(i))/(x(i+1)-x(i))-(y(i)-y(i-1)) |
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| 44 | |
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| 45 | . /(x(i)-x(i-1)))/(x(i+1)-x(i-1))-sig*u(i-1))/p |
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| 46 | |
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| 47 | 11 continue |
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| 48 | |
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| 49 | if(ypn.gt.0.99E30) then |
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| 50 | c the upper boundary condition is set |
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| 51 | qn=0. |
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| 52 | c either to be "natural" |
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| 53 | un=0. |
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| 54 | |
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| 55 | else |
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| 56 | c or else to have a specified first |
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| 57 | qn=0.5 |
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| 58 | c derivative |
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| 59 | un=(3./(x(n)-x(n-1)))*(ypn-(y(n)-y(n-1))/(x(n)-x(n-1))) |
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| 60 | |
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| 61 | end if |
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| 62 | |
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| 63 | y2(n)=(un-qn*u(n-1))/(qn*y2(n-1)+1.) |
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| 64 | |
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| 65 | do 12 k=n-1,1,-1 |
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| 66 | c this is the backsubstitution loop of |
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| 67 | y2(k)=y2(k)*y2(k+1)+u(k) |
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| 68 | c the tridiagonal algorithm |
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| 69 | 12 continue |
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| 70 | |
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| 71 | c |
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| 72 | |
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| 73 | return |
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| 74 | |
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| 75 | end |
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| 76 | |
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