Primitive function
anti-derivative, of a finite function
A function such that
everywhere in the domain of definition of
. This definition is the one most widely used, but others occur, in which the requirements on the existence of a finite
everywhere are weakened, as are those on the equation
everywhere; a generalized derivative is sometimes used in the definition. Most of the theorems on primitive functions concern their existence, determination and uniqueness. A sufficient condition for the existence of a primitive function of a function
given on an interval is that
is continuous; necessary conditions are that
should belong to the first Baire class (cf. Baire classes) and that it has the Darboux property. Any two primitive functions of a function given on an interval differ by a constant. The task of finding
from
for continuous
is solved by the Riemann integral, for bounded
— by the Lebesgue integral, and for any
— by the Denjoy integral in the narrow (or wide) sense and the Perron integral.
References
[1] | L.D. Kudryavtsev, "A course in mathematical analysis" , 1 , Moscow (1981) (In Russian) |
[2] | S.M. Nikol'skii, "A course of mathematical analysis" , 1 , MIR (1977) (Translated from Russian) |
Comments
The Darboux property or intermediate-value property of a real-valued function on an interval
says that if
and
are two values of
,
, then
assumes any value between
and
at some point between
and
. Continuous functions have the intermediate-value property (the intermediate-value theorem). The fact that the derivative of a one-time differentiable real-valued function on an interval has the intermediate-value property is sometimes referred to as Darboux's theorem. It is an immediate consequence of the Rolle theorem.
See also (the editorial comments to) Derivative.
References
[a1] | R.P Boas jr., "A primer of real functions" , Math. Assoc. Amer. (1981) |
[a2] | T.M. Apostol, "Mathematical analysis" , Addison-Wesley (1974) |
Primitive function. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Primitive_function&oldid=18563