Evaluate the supplied function once at each positive integer, retaining its largest value so far. In particular do not initialize the maximum to zero: might be negative everywhere.At the loop head the loop invariant is ,
PROCEDURE record(f, emit);
VAR n, best, y: INTEGER;
BEGIN
best := f(1);
emit(1);
n := 2;
WHILE TRUE DO
y := f(n);
IF y > best THEN
emit(n);
best := y
END;
n := n + 1
END
END record;best , and precisely the record values with argument less than have been emitted, in increasing argument order. The first argument is a record because its comparison set is empty. The strict test correctly excludes ties. Updating best only on a strict increase preserves the loop invariant.Exactly one call of
f is made per processed argument. For an arbitrary supplied function, an unexamined argument can have a value larger than all previous values, so skipping its evaluation cannot be correct in general. This assumes is a total, deterministic function; the requested infinite computation ignores integer overflow. Articles by others on the same topic
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