Such a function is called a (smooth) cutoff function; these are used to eliminate singularities of a given (generalized) function via multiplication. They leave unchanged the value of the multiplicand on a given set, but modify its support. Why use "smooth cutoff functions" If we only want to use values of for we could use inside this interval, and zero outside.
But this gives a function with jumps, and the Fourier transform has oscillations and slow decay like (Gibbs phenomenon). In several applications we can avoid this problem by using smoother cutoff functions. Cutoff function with controlled derivative Ask Question Asked 8 years, 9 months ago Modified 8 years, 9 months ago.
A cut-off function with controlled gradient Ask Question Asked 8 years, 2 months ago Modified 8 years ago. Download scientific diagram The smooth cutoff function used to extend the restriction of X to D L to R 3 periodically. from publication: A practical use of the Melnikov homoclinic method Using.
In partial differential equations, the introduction of cut-off function is an important mean to localize the problem, which can not only preserve the local property of the truncated function, but also effectively avoid the influence of various factors outside the small neighborhood. In this paper, we first introduce the mollification, then an important property of cut. Keywords Smooth Function Closed Subset Open Ball Require Function Countable Collection These keywords were added by machine and not by the authors.
This process is experimental and the keywords may be updated as the learning algorithm improves. Bump functions are often used as mollifiers, as smooth cutoff functions, and to form smooth partitions of unity. They are the most common class of test functions used in analysis.
A common way to construct a smooth cutoff function is to take the convolution of a characteristic function (AKA indicator function) with a mollifier or an approximate identity, and use the fact that this convolution approximates the original function pointwise under suitable assumptions. Smooth Cutoff Functions By convolution of the characteristic function of the unit ball with the smooth function (defined as in (3) with), one obtains the function which is a smooth function equal to on, with support contained in. This can be seen easily by observing that if ≤ and ≤ then ≤.
Hence for ≤,. It is easy to see how this construction can be generalized to obtain a smooth.