Τι (ποιος) είναι partial evaluation - ορισμός
TECHNIQUE FOR PROGRAM OPTIMIZATION
Partial Evaluation; Futamura projection; Partial evaluator; Yoshihiko Futamura
partial evaluation
<compiler, algorithm> (Or "specialisation") An optimisation
technique where the compiler evaluates some subexpressions
at compile-time. For example,
pow x 0 = 1
pow x n = if even n
then pxn2 * pxn2
else x * pow x (n-1)
where pxn2 = pow x (n/2)
f x = pow x 5
Since n is known we can specialise pow in its second argument
and unfold the recursive calls:
pow5 x = x * x4 where x4 = x2 * x2
x2 = x * x
f x = pow5 x
pow5 is known as the residual. We could now also unfold pow5
giving:
f x = x * x4 where x4 = x2 * x2
x2 = x * x
It is important that the partial evaluation algorithm should
terminate. This is not guaranteed in the presence of
recursive function definitions. For example, if partial
evaluation were applied to the right hand side of the second
clause for pow above, it would never terminate because the
value of n is not known.
Partial evaluation might change the termination properties of
the program if, for example, the expression (x * 0) was
reduced to 0 it would terminate even if x (and thus x * 0) did
not.
It may be necessary to reorder an expression to partially
evaluate it, e.g.
f x y = (x + y) + 1
g z = f 3 z
If we rewrite f:
f x y = (x + 1) + y
then the expression x+1 becomes a constant for the function g
and we can say
g z = f 3 z = (3 + 1) + z = 4 + z
Partial evaluation of built-in functions applied to constant
arguments is known as constant folding.
See also full laziness.
(1999-05-25)
Partial evaluation
In computing, partial evaluation is a technique for several different types of program optimization by specialization. The most straightforward application is to produce new programs that run faster than the originals while being guaranteed to behave in the same way.
Partial derivative
DERIVATIVE OF A FUNCTION OF SEVERAL VARIABLES WITH RESPECT TO ONE VARIABLE, WITH THE OTHERS HELD CONSTANT
Partial Derivatives; Partial derivatives; Partial differentiation; Partial derivation; Mixed partial derivatives; Mixed derivatives; Partial Derivative; Mixed partial derivative; Partial differential; Partial symbol; Partial differentiation; Del (∂); Cross derivative
In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant (as opposed to the total derivative, in which all variables are allowed to vary). Partial derivatives are used in vector calculus and differential geometry.
Βικιπαίδεια
Partial evaluation
In computing, partial evaluation is a technique for several different types of program optimization by specialization. The most straightforward application is to produce new programs that run faster than the originals while being guaranteed to behave in the same way.
A computer program prog is seen as a mapping of input data into output data:
where , the static data, is the part of the input data known at compile time.
The partial evaluator transforms into by precomputing all static input at compile time. is called the "residual program" and should run more efficiently than the original program. The act of partial evaluation is said to "residualize" to .
