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+c function pbinom.f
+c
+c source
+c   Bevington, page 31.
+c
+c purpose
+c   evaluate binomial probability coefficient
+c
+c usage
+c   result = pbinom (nobs, ntotal, prob)
+c
+c description of parameters
+c   nobs   - number of items observed
+c   ntotal - total number of items
+c   prob   - probability of observing each item
+c
+c subroutines and function subprograms required
+c   factor (n)
+c      calculates n factorial for integers
+c
+      function pbinom (nobs,ntotal,prob)
+1     notobs=ntotal-nobs
+2     pbinom=factor(ntotal)/(factor(nobs)*factor(notobs))*
+     *       (prob**nobs)*(1.-prob)**notobs
+      return
+      end