September 2017 Update

Task/Van-der-Corput-sequence/Fortran/van-der-corput-sequence.f

@@ -0,0 +1,35 @@
+      FUNCTION VDC(N,BASE)	!Calculates a Van der Corput number...
+Converts 1234 in decimal to 4321 in V, and P = 10000.
+       INTEGER N	!For this integer,
+       INTEGER BASE	!In this base.
+       INTEGER I	!A copy of N that can be damaged.
+       INTEGER P	!Successive powers of BASE.
+       INTEGER V	!Accumulates digits.
+        P = 1		! = BASE**0
+        V = 0		!Start with no digits, as if N = 0.
+        I = N		!Here we go.
+        DO WHILE (I .NE. 0)	!While something remains,
+          V = V*BASE + MOD(I,BASE)	!Extract its low-order digit.
+          I = I/BASE			!Reduce it by a power.
+          P = P*BASE			!And track the power.
+        END DO			!Thus extract the digits in reverse order: right-to-left.
+        VDC = V/FLOAT(P)	!The power is one above the highest digit.
+      END FUNCTION VDC	!Numerology is weird.
+
+      PROGRAM POKE
+      INTEGER FIRST,LAST	!Might as well document some constants.
+      PARAMETER (FIRST = 0,LAST = 9)	!Thus, the first ten values.
+      INTEGER I,BASE		!Steppers.
+      REAL VDC			!Stop the compiler moaning about undeclared items.
+
+      WRITE (6,1) FIRST,LAST,(I, I = FIRST,LAST)	!Announce.
+    1 FORMAT ("Calculates values ",I0," to ",I0," of the ",
+     1 "Van der Corput sequence, in various bases."/
+     2 "Base",666I9)
+
+      DO BASE = 2,13	!A selection of bases.
+        WRITE (6,2) BASE,(VDC(I,BASE), I = FIRST,LAST)	!Show the specified span.
+    2   FORMAT (I4,666F9.6)	!Aligns with FORMAT 1.
+      END DO		!On to the next base.
+
+      END