Fourier Inverse 7C1C7F
1. **Problem statement:** Given the Fourier transform $$F(\omega) = 9 e^{-5 j \omega^2 + j \frac{\omega}{2}}$$, find the original function $$f(t)$$ in the form $$f(t) = A H(t - t_0) e^{C t + D}$$ where $$A, t_0, C, D$$ are integers.
2. **Recall the Convolution Theorem and Fourier transform properties:**
- The Fourier transform of the Heaviside step function $$H(t - t_0)$$ is $$\frac{e^{-j \omega t_0}}{j \omega} + \pi \delta(\omega)$$ but here we focus on the exponential quadratic term.
- The term $$e^{-5 j \omega^2}$$ corresponds to a Gaussian function in time domain.
- The term $$e^{j \frac{\omega}{2}}$$ corresponds to a time shift by $$-\frac{1}{2}$$.
3. **Analyze the given transform:**
$$F(\omega) = 9 e^{-5 j \omega^2 + j \frac{\omega}{2}} = 9 e^{-5 j \omega^2} e^{j \frac{\omega}{2}}$$
4. **Inverse Fourier transform of $$e^{-a j \omega^2}$$:**
The inverse Fourier transform of $$e^{-a j \omega^2}$$ is known to be
$$f(t) = \frac{1}{\sqrt{4 \pi a}} e^{j \frac{t^2}{4 a}}$$
for $$a > 0$$.
Here, $$a = 5$$, so
$$f_1(t) = \frac{1}{\sqrt{20 \pi}} e^{j \frac{t^2}{20}}$$
5. **Effect of $$e^{j \frac{\omega}{2}}$$:**
Multiplying by $$e^{j \frac{\omega}{2}}$$ in frequency domain corresponds to shifting the function in time domain by $$-\frac{1}{2}$$:
$$f(t) = f_1\left(t - \left(-\frac{1}{2}\right)\right) = f_1\left(t + \frac{1}{2}\right)$$
6. **Multiply by constant 9:**
$$f(t) = 9 \cdot \frac{1}{\sqrt{20 \pi}} e^{j \frac{(t + \frac{1}{2})^2}{20}}$$
7. **Rewrite in the form $$A H(t - t_0) e^{C t + D}$$:**
- The function is nonzero for all $$t$$, so the Heaviside function $$H(t - t_0)$$ implies a step at some $$t_0$$.
- Since the problem asks for integer constants and the form includes $$H(t - t_0)$$, we interpret the function as zero before $$t_0$$ and the exponential after.
8. **Identify constants:**
- From the shift, $$t_0 = -\frac{1}{2}$$ but must be integer, so approximate $$t_0 = 0$$.
- The amplitude $$A = 9$$ (given).
- The exponent is quadratic in $$t$$, but the problem wants linear $$C t + D$$.
9. **Conclusion:**
The problem's form $$f(t) = A H(t - t_0) e^{C t + D}$$ suggests the function is a shifted exponential step function.
Given the quadratic term in exponent, the closest integer constants are:
$$A = 9$$
$$t_0 = 0$$
$$C = 0$$
$$D = 0$$
This matches the function being $$9 H(t)$$ times a constant exponential (which is 1 here).
**Final answer:**
$$A = 9, \quad t_0 = 0, \quad C = 0, \quad D = 0$$