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@@ -7134,48 +7134,45 @@ sufficient hooks for the user to define her own force functions.)" |
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(reorder-internal
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variables cost-function terminate? order force-function))))
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-;;; FIXME: This doesn't make any sense. See branch "maybe" for an alternative
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-;;; expression. Also: why are we trying to increase the upper bound, and not
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-;;; the lower bound? Should the API also not allow us to minimize a variable
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-;;; towards either zero or negative infinity? --ns 2011-11-01
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+;;; FIXME: What about optimizing towards negative infinity or zero? What
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+;;; about restricting the low bound? What are the real applications for this?
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+;;; What about evaluations that provide eg. a low bound higher than the
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+;;; previous high bound, but no high bound?
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(defmacro-compile-time best-value
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- (form1 objective-form &optional (form2 nil form2?))
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- "First evaluates OBJECTIVE-FORM, which should evaluate to constraint variable V.
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-
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-Then repeatedly evaluates FORM1 in non-deterministic context till it fails. If
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-previous round of evaluation produced an upper bound B for V, the during the
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-next round any change to V must provide an upper bound higher than B, or that
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-that change fails.
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-
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-If the last successful evaluation of FORM produced an upper bound for V,
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-returns a list of two elements: the the primary value of FORM1 from that
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-round, and the upper bound of V.
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-
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-Otherwise if FORM2 is provided, returns the result of evaluating it, or else
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-calls fails.
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-
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-Note: this documentation string is entirely reverse-engineered. Lacking
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-information on just how BEST-VALUE was intended to work, it is hard to tell
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-what is a bug, an accident of implementation, and what is a feature. If you
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-have any insight into BEST-VALUE, please send email to
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-nikodemus@random-state.net."
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- (let ((bound (gensym "BOUND-"))
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- (best (gensym "BEST-"))
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- (objective (gensym "OBJECTIVE-")))
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+ (form objective &optional (default '(fail)))
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+ "Evaluates OBJECTIVE, which should evaluate to real-valued
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+constraint variable V.
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+
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+Then repeatedly evaluates FORM in non-deterministic context till it
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+fails. Once a successful evaluation has produced an upper bound for V,
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+any subsequent evaluation of FORM that restricts the upper bound of V
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+to less than or equal the previous upper bound fails.
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+
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+If any evaluation produced an upper bound for V, returns a list of two
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+elements: the the primary value of FORM from the evaluation where
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+upper bound of V reached its maximum, and that upper bound.
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+
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+Otherwise evaluates DEFAULT -- defaulting to FAIL."
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+ (let ((bound (gensym "BOUND"))
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+ (best (gensym "BEST"))
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+ (objectivev (gensym "OBJECTIVE")))
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`(let ((,bound nil)
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(,best nil)
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- (,objective (variablize ,objective-form)))
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+ (,objectivev (variablize ,objective)))
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(attach-noticer!
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#'(lambda ()
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- (let ((upper (variable-upper-bound ,objective)))
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+ (let ((upper (variable-upper-bound ,objectivev)))
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(when (and ,bound upper (<= upper ,bound))
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(fail))))
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- ,objective)
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+ ,objectivev)
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(for-effects
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- (let ((value ,form1))
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- (global (setf ,bound (variable-upper-bound ,objective))
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- (setf ,best value))))
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- (if ,bound (list ,best ,bound) ,(if form2? form2 '(fail))))))
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+ (let ((value ,form)
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+ (tmp (variable-upper-bound ,objectivev)))
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+ (when tmp
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+ (global
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+ (setf ,bound tmp)
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+ (setf ,best value)))))
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+ (if ,bound (list ,best ,bound) ,default))))
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(defun template-internal (template variables)
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(cond
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