With respect to the range of convergence of the Laplace
integral
(A.1)
now the following considerations are taken:
If the function to be transformed is stepwise continuous
and if there are real numbers and
such
that for all
is valid, then the Laplace integral will converge for all with
. Particularly, if for
the smallest possible value
is taken, the condition
is the smallest possible convergence range.
Consequently the Laplace integral exists only within some part of
the complex plane. This
part is called convergence area, as shown in Figure A.1. The
variable
is called
Figure A.1:
Convergence area of the Laplace integral
the abscissa of
convergence.
For values of with
Eq. (A.1) makes no sense.
Thus for
the limit value of
for
must go to zero, but not for
.
Example A.1.1
The Laplace integral converges for all with
, as
for
decreases faster than any
power of increases.