in:

• :

  is the technological correlation between company i and company j in period t, with a value range of [-1, 1]. The higher the value, the higher the technological correlation between the two companies.

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  is the N-dimensional patent distribution vector of company i in period t, where N represents the total number of technology categories defined by the Patent and Trademark Office. Each element of this vector represents the proportion of each type of technology patent obtained by company i in the corresponding technology category in the past five years. More specifically, $T_{it}$ = [$t_{i1t}$, $t_{i2t}$, ..., $t_{iNt}$], where $t_{ikt}$ represents the proportion of patents in the k-th technology category of company i at time t. The calculation of this vector takes into account the company's patent layout in different technical fields.

• :

  Represents the Euclidean norm (or L2 norm) of the vector $T_{it}$, that is, $\sqrt{T_{it} \cdot T_{it}}$. It is used to standardize the patent distribution vector to avoid the deviation in correlation calculation caused by different numbers of patents.

• :

  is the rate of return of company j in period t, usually refers to the arithmetic rate of return of the stock, that is, $RET_{jt} = \frac{P_{jt} - P_{j(t-1)}}{P_{j(t-1)}}$, where $P_{jt}$ is the stock price of company j in period t.