Initial commit

2016-02-03 18:52:05 +00:00
commit d40505e161
507 changed files with 91383 additions and 0 deletions
@@ -0,0 +1,56 @@
+      FUNCTION expint(n,x)
+      INTEGER n,MAXIT
+      REAL expint,x,EPS,FPMIN,EULER
+      PARAMETER (MAXIT=100,EPS=1.e-7,FPMIN=1.e-30,EULER=.5772156649)
+      INTEGER i,ii,nm1
+      REAL a,b,c,d,del,fact,h,psi
+      nm1=n-1
+      if(n.lt.0.or.x.lt.0..or.(x.eq.0..and.(n.eq.0.or.n.eq.1)))then
+        pause 'bad arguments in expint'
+      else if(n.eq.0)then
+        expint=exp(-x)/x
+      else if(x.eq.0.)then
+        expint=1./nm1
+      else if(x.gt.1.)then
+        b=x+n
+        c=1./FPMIN
+        d=1./b
+        h=d
+        do 11 i=1,MAXIT
+          a=-i*(nm1+i)
+          b=b+2.
+          d=1./(a*d+b)
+          c=b+a/c
+          del=c*d
+          h=h*del
+          if(abs(del-1.).lt.EPS)then
+            expint=h*exp(-x)
+            return
+          endif
+11      continue
+        pause 'continued fraction failed in expint'
+      else
+        if(nm1.ne.0)then
+          expint=1./nm1
+        else
+          expint=-log(x)-EULER
+        endif
+        fact=1.
+        do 13 i=1,MAXIT
+          fact=-fact*x/i
+          if(i.ne.nm1)then
+            del=-fact/(i-nm1)
+          else
+            psi=-EULER
+            do 12 ii=1,nm1
+              psi=psi+1./ii
+12          continue
+            del=fact*(-log(x)+psi)
+          endif
+          expint=expint+del
+          if(abs(del).lt.abs(expint)*EPS) return
+13      continue
+        pause 'series failed in expint'
+      endif
+      return
+      END