Repatch (from linux) of OSX IRAF

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
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+++ b/math/bevington/xfit.f
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+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