blob: 65576bb6aa22b23f53ecd580971c148a70ffadbe (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
|
\subsection{Proof of support recovery lemma}
\subsection{Upper-bound for $\|\nabla f(\theta^*)\|_\infty$}
We show an upper-bound for $ 2 \|\nabla f(\theta^*) \|_\infty$. If we only consider the first measurement of every cascade, this can be done easily. Let $N$ be the number of cascades (to distinguish from $n$ number of total measurements). Begin by noting that for a node $\alpha$:
\begin{align}
\nabla_k f(\theta) & = \sum^n_{i=1} \frac{b^i x^i_k}{1 - e^{\langle x^i, \theta \rangle}} - \sum^n_{i=1} x^i_k \nonumber \\
& = \sum_{i=1}^n x^k_i \left( \frac{b^i}{\mathbb{P}(\text{node } \alpha \text { infected})} - 1\right) \nonumber
\end{align}
\begin{lemma}
\label{lem:subgaussian_variable}
$\nabla f(\theta^*)$ is a $N/p_{\min}$-subgaussian variable, where $p_{\min}$ is the smallest non-zero link to node $\alpha$.
\end{lemma}
\begin{proof}
We show that its expectation is $0$ by conditioning on the seed set $S$:
\begin{align}
\mathbb{E} \left( \nabla_k f(\theta) \right) & = \sum_{i=1}^N \mathbb{E} \left[ x^i_k \left( \frac{b^i}{\mathbb{P}(\alpha \text { infected})} - 1\right) \right] \nonumber \\
& = \sum_{i=1}^N \mathbb{E}_S \left[ \mathbb{E}\left[x^i_k \left( \frac{b^i}{\mathbb{P}(\alpha \text { infected})} - 1\right) \middle| S \right] \right] \nonumber \\
& = \sum_{i=1}^N \mathbb{E}\left[x^i_k \left( \frac{ \mathbb{E}_S \left[ b^i \middle| S \right]}{\mathbb{P}(\alpha \text { infected})} - 1\right) \right] \nonumber \\
& = 0 \nonumber
\end{align}
Therefore, $\nabla f(\theta^*)$ is the sum of zero-mean variables, upper-bounded by $1/p_{\min}$. It follows that $\nabla f(\theta^*)$ is $N/p_{\min}$-subgaussian.
\end{proof}
By union bound and characterization of sub-gaussian variables:
\begin{equation}
\mathbb{P}(\| \nabla f(\theta) \|_{\infty} > \lambda) \leq 2 \exp \left( -\frac{\lambda^2 p_{\min}}{2n} + \log m \right)
\end{equation}
In conclusion, for $\delta>0$, $\lambda := 2 \sqrt{\frac{n^{\delta + 1} \log m}{p_{\min}}}$ is a valid regularizer with probability $1 - \exp(-n^\delta \log m )$
|
