Initial data commit

Task/Forward-difference/XPL0/forward-difference.xpl0

@@ -0,0 +1,32 @@
+\Calculate forward differences
+
+\Sets elements of B to the first order forward differences of A.
+\A should have bounds 1 :: N, B should have bounds 1 :: N - 1.
+procedure FirstOrderFDifference ( A, B, N );
+integer A, B, N, I;
+for I := 2 to N do B( I - 1 ) := A( I ) - A( I - 1 );
+
+integer V   ( 1 + 10 );
+integer Diff( 1 +  9 );
+integer VPos, Length, List, I, Order;
+begin
+    \construct the initial values array
+    VPos := 1;
+    List:= [90, 47, 58, 29, 22, 32, 55, 5, 55, 73];
+    for I := 0 to 10-1 do begin
+        V( VPos ) := List( I );
+        VPos := VPos + 1
+    end;
+
+    \calculate and show the differences
+    Format(8, 0);       \set output format
+    Length := 10;
+    for Order := 1 to Length - 1 do begin
+        FirstOrderFDifference( V, Diff, Length );
+        Length := Length - 1;
+        IntOut(0, Order);  Text(0, " : ");
+        for I := 1 to Length do RlOut(0, float(Diff( I ) ));
+        CrLf(0);
+        for I := 1 to Length do V( I ) := Diff( I )
+    end
+end