new files

Task/Entropy/REXX/entropy-1.rexx

@@ -0,0 +1,84 @@
+/* Rexx ***************************************************************
+* 28.02.2013 Walter Pachl
+* 12.03.2013 Walter Pachl  typo in log corrected. thanx for testing
+**********************************************************************/
+s="1223334444"
+occ.=0
+n=0
+Do i=1 To length(s)
+  c=substr(s,i,1)
+  occ.c=occ.c+1
+  n=n+1
+  End
+do c=1 To 4
+  p.c=occ.c/n
+  say c p.c
+  End
+e=0
+Do c=1 To 4
+  e=e+p.c*log(p.c,,2)
+  End
+Say 'Entropy of' s 'is' (-e)
+Exit
+
+log: Procedure
+/***********************************************************************
+* Return log(x) -- with specified precision and a specified base
+* Three different series are used for the ranges  0 to 0.5
+*                                                 0.5 to 1.5
+*                                                 1.5 to infinity
+* 03.09.1992 Walter Pachl
+***********************************************************************/
+  Parse Arg x,prec,b
+  If prec='' Then prec=9
+  Numeric Digits (2*prec)
+  Numeric Fuzz   3
+  Select
+    When x<=0 Then r='*** invalid argument ***'
+    When x<0.5 Then Do
+      z=(x-1)/(x+1)
+      o=z
+      r=z
+      k=1
+      Do i=3 By 2
+        ra=r
+        k=k+1
+        o=o*z*z
+        r=r+o/i
+        If r=ra Then Leave
+        End
+      r=2*r
+      End
+    When x<1.5 Then Do
+      z=(x-1)
+      o=z
+      r=z
+      k=1
+      Do i=2 By 1
+        ra=r
+        k=k+1
+        o=-o*z
+        r=r+o/i
+        If r=ra Then Leave
+        End
+      End
+    Otherwise /* 1.5<=x */ Do
+      z=(x+1)/(x-1)
+      o=1/z
+      r=o
+      k=1
+      Do i=3 By 2
+        ra=r
+        k=k+1
+        o=o/(z*z)
+        r=r+o/i
+        If r=ra Then Leave
+        End
+      r=2*r
+      End
+    End
+  If b<>'' Then
+    r=r/log(b)
+  Numeric Digits (prec)
+  r=r+0
+  Return r