Initial commit

2016-02-03 18:52:05 +00:00
commit d40505e161
507 changed files with 91383 additions and 0 deletions
@@ -0,0 +1,38 @@
+      FUNCTION ei(x)
+      INTEGER MAXIT
+      REAL ei,x,EPS,EULER,FPMIN
+      PARAMETER (EPS=6.e-8,EULER=.57721566,MAXIT=100,FPMIN=1.e-30)
+      INTEGER k
+      REAL fact,prev,sum,term
+      if(x.le.0.) pause 'bad argument in ei'
+      if(x.lt.FPMIN)then
+        ei=log(x)+EULER
+      else if(x.le.-log(EPS))then
+        sum=0.
+        fact=1.
+        do 11 k=1,MAXIT
+          fact=fact*x/k
+          term=fact/k
+          sum=sum+term
+          if(term.lt.EPS*sum)goto 1
+11      continue
+        pause 'series failed in ei'
+1       ei=sum+log(x)+EULER
+      else
+        sum=0.
+        term=1.
+        do 12 k=1,MAXIT
+          prev=term
+          term=term*k/x
+          if(term.lt.EPS)goto 2
+          if(term.lt.prev)then
+            sum=sum+term
+          else
+            sum=sum-prev
+            goto 2
+          endif
+12      continue
+2       ei=exp(x)*(1.+sum)/x
+      endif
+      return
+      END