- #1
Irid
- 207
- 1
Hello,
I was wondering if such a thing even exists, so here it goes... Let's say I have a function x(s) (it is real, smooth, differentiable, etc.) defined on (0,1). In addition, dx/ds = 0 on the boundary (s=0 and s=1). I can compute its Fourier transform (?) as
[tex] a_p = \int_0^1 x(s) \cos(sp\pi)\, ds [/tex]
and now I have a set of numbers [itex]a_p[/itex] which contain the same information as the original function x(s).
The good news is that if I compute the same Fourier transform on the derivatives of x, i.e.
[tex] \int_0^1 \frac{d^2 x}{ds^2} \cos(sp\pi)\, ds = -p^2 \pi^2 a_p[/tex]
I get an answer in terms of the [itex]a_p[/itex] which I already know.
So here's my question:
What if I want to find the Fourier transform of higher powers of x?
[tex] \int_0^1 x^2 \cos(sp\pi)\, ds =\, ? [/tex]
Can it be expressed in terms of, let's say, a power series in [itex]a_p[/itex]?
[tex] \int_0^1 x^2 \cos(sp\pi)\, ds =\, ?\, \sum_{n=0}^{\infty} c_n a_p^n[/tex]
And what if I want to find the Fourier transform of a generic functional f[x(s)] (smooth, differentiable, etc.)? Is it related somehow to the Fourier transform of the original function x(s)?
I was wondering if such a thing even exists, so here it goes... Let's say I have a function x(s) (it is real, smooth, differentiable, etc.) defined on (0,1). In addition, dx/ds = 0 on the boundary (s=0 and s=1). I can compute its Fourier transform (?) as
[tex] a_p = \int_0^1 x(s) \cos(sp\pi)\, ds [/tex]
and now I have a set of numbers [itex]a_p[/itex] which contain the same information as the original function x(s).
The good news is that if I compute the same Fourier transform on the derivatives of x, i.e.
[tex] \int_0^1 \frac{d^2 x}{ds^2} \cos(sp\pi)\, ds = -p^2 \pi^2 a_p[/tex]
I get an answer in terms of the [itex]a_p[/itex] which I already know.
So here's my question:
What if I want to find the Fourier transform of higher powers of x?
[tex] \int_0^1 x^2 \cos(sp\pi)\, ds =\, ? [/tex]
Can it be expressed in terms of, let's say, a power series in [itex]a_p[/itex]?
[tex] \int_0^1 x^2 \cos(sp\pi)\, ds =\, ?\, \sum_{n=0}^{\infty} c_n a_p^n[/tex]
And what if I want to find the Fourier transform of a generic functional f[x(s)] (smooth, differentiable, etc.)? Is it related somehow to the Fourier transform of the original function x(s)?