This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.

Dynamic

 Dynamic[expr]represents an object that displays as the dynamically updated current value of expr. If the displayed form of Dynamic[expr] is interactively changed or edited, an assignment expr=val is done to give expr the new value val that corresponds to the displayed form. Dynamic[expr, None]does not allow interactive changing or editing. Dynamic[expr, f]continually evaluates f[val, expr] during interactive changing or editing of val. Dynamic[expr, {f, fend}]also evaluates fend[val, expr] when interactive changing or editing is complete. Dynamic[expr, {fstart, f, fend}]also evaluates fstart[val, expr] when interactive changing or editing begins.
• Dynamic[expr] can appear not only directly as an expression to display, but also for example as a coordinate in a graphics primitive or an object such as a slider, or as a setting for an option.
• When used to assign values to expr through interactive operations, the expression in Dynamic[expr] will most often be a symbol x, an object x[i], a part e[[i]] or a list {x, y, ...}.
• In graphics for example, Point[Dynamic[{x, y}]] represents a point whose position is dynamically updated to be given by the current values of x and y. Whenever the point is interactively moved, assignments of the form {x, y}={valx, valy} are done. Point[Dynamic[{x, y}]] can be moved interactively; Dynamic[Point[{x, y}]] cannot.
• Dynamic[expr] evaluates expr whenever it needs its value and it determines that any type of value of symbols on which it depends might have changed.
• If Refresh or Clock objects appear in the evaluation of the expression in Dynamic[expr], then expr will always continually be re-evaluated.
• Dynamic has attribute HoldFirst, so that expr is not evaluated until its value is needed for display.
• Dynamic[expr, f] makes interactive operations not change expr except by virtue of the evaluation of f[val, expr].
• Objects represented by Dynamic[expr, None] cannot be changed interactively, but will change if the value of expr changes for other reasons.
• Dynamic[expr, Temporary] allows the displayed form of an object to change in the course of interactive operations, but assigns an updated value to expr only when the operations are complete.
• For interactive mouse operations Dynamic[expr, {fstart, f, fend}] typically evaluates fstart[val, expr] once when the mouse is pressed, then evaluates f[val, expr] whenever the mouse is moved, and then evaluates fend[val, expr] once when the mouse is released.
• If the mouse is not moved, fstart, f and fend are each evaluated exactly once.
• f[val, expr] is always evaluated once immediately after the evaluation of fstart[val, expr], and when it is last evaluated, the value of val is always the same as in fend[val, expr].
• Interactive operations that can affect Dynamic objects include dragging of elements in graphics or in objects such as Slider, as well as editing of fields in objects such as InputField.
• The functions fstart, f and fend can be the following:
 Automatic assign values using Set None perform no action Temporary allow interactive operations to make temporary changes func evaluate func[val, expr]
• Dynamic[expr, f] can be used to enforce constraints on values assigned to expr.
• Dynamic[expr, f] can be used to do assignments for individual variables when expr is an expression like x+y.
• A function func[val, expr] should have attribute HoldRest if it is going to perform an assignment to expr. This can be achieved with Function[{v, e}, body, HoldRest].
• The following options can be given:
 Deinitialization None an expression to evaluate when the Dynamic can no longer be displayed Editable False whether to allow the textual display of Dynamic to be edited Evaluator Automatic the kernel to use for evaluations Initialization None an expression to evaluate when the Dynamic is first displayed ShrinkingDelay 0. how long to delay before shrinking if the displayed object gets smaller TrackedSymbols Automatic symbols whose changes trigger an update UpdateInterval Infinity time interval at which to do updates
• Dynamic[expr] provides an analog of delayed assignment, where values are implicitly requested by the need to display, rather than by evaluation of an expression.
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