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Diffstat (limited to 'math/bevington/xfit.f')
| -rw-r--r-- | math/bevington/xfit.f | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/math/bevington/xfit.f b/math/bevington/xfit.f new file mode 100644 index 00000000..a097d4af --- /dev/null +++ b/math/bevington/xfit.f @@ -0,0 +1,59 @@ +c subroutine xfit.f +c +c source +c Bevington, page 76. +c +c purpose +c calculate the mean and estimated errors for a set of data points +c +c usage +c call xfit (x, sigmax, npts, mode, xmean, sigmam, sigma) +c +c description of parameters +c x - array of data points +c sigmax - array of standard deviations for data points +c npts - number of data points +c mode - determines method of weighting +c +1 (instrumental) weight(i) = 1./sigmax(i)**2 +c 0 (no weighting) weight(i) = 1. +c -1 (statistical) weight(i) = 1. +c xmean - weighted mean +c sigmam - standard deviation of mean +c sigma - standard deviation of data +c +c subroutines and function subprograms required +c none +c + subroutine xfit (x,sigmax,npts,mode,xmean,sigmam,sigma) + double precision sum,sumx,weight,free + dimension x(1),sigmax(1) +c +c accumulate weighted sums +c +11 sum=0. + sumx=0. + sigma=0. + sigmam=0. +20 do 32 i=1,npts +21 if (mode) 22,22,24 +22 weight=1. + goto 31 +24 weight=1./sigmax(i)**2 +31 sum=sum+weight +32 sumx=sumx+weight*x(i) +c +c evaluate mean and standard deviations +c +41 xmean=sumx/sum +51 do 52 i=1,npts +52 sigma=sigma+(x(i)-xmean)**2 + free=npts-1 +54 sigma=dsqrt(sigma/free) +61 if (mode) 62,64,66 +62 sigmam=dsqrt(xmean/sum) + goto 70 +64 sigmam=sigma/dsqrt(sum) + goto 70 +66 sigmam=dsqrt(1./sum) +70 return + end |