45 lines
1.0 KiB
FortranFixed
45 lines
1.0 KiB
FortranFixed
subroutine y_aPLUSbx(npoints0,x0,y0,a,b)
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implicit none
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!fit for y=a+bx
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integer npoints0
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double precision x0(npoints0),y0(npoints0),a,b
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integer i,npoints
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double precision xmean,ymean,lxx,lyy,lxy,fn9999,tiny,
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&x(npoints0),y(npoints0)
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parameter(fn9999=-9999.0d0,tiny=1.0d-7)
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npoints=0
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do i=1,npoints0
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if(dabs(x0(i)-fn9999).gt.tiny.and.
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&dabs(y0(i)-fn9999).gt.tiny)then
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npoints=npoints+1
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x(npoints)=x0(i)
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y(npoints)=y0(i)
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endif
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enddo
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xmean=0.0d0
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ymean=0.0d0
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do i=1,npoints
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xmean=xmean+x(i)
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ymean=ymean+y(i)
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enddo
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xmean=xmean/dble(npoints)
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ymean=ymean/dble(npoints)
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lxx=0.0d0
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lyy=0.0d0
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lxy=0.0d0
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do i=1,npoints
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lxx=lxx+(x(i)-xmean)**2
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lyy=lyy+(y(i)-ymean)**2
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lxy=lxy+(x(i)-xmean)*(y(i)-ymean)
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enddo
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if(lxx.ne.0.0d0)then
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b=lxy/lxx
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a=ymean-b*xmean
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else
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b=-9999.0d0
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a=-9999.0d0
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endif
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return
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end
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