**Daily update | 21 May, 2022**

# StackExchange

#### Is the sum of two singular covariance matrices also singular?

**Source:** stats**Views:** 167**Score:** 6**Tags:** covariance-matrix sum singular

#### Is the set of languages satisfying the pumping lemma closed under concatenation?

**Source:** cs**Views:** 107**Score:** 3**Tags:** regular-languages pumping-lemma closure-properties

#### Exists an option to avoid reference categories in logistic regression?

**Source:** stats**Views:** 108**Score:** 3**Tags:** regression logistic categorical-encoding

#### Objective criteria for assumption violations that do not utilize p-values?

**Source:** stats**Views:** 33**Score:** 2**Tags:** hypothesis-testing references linear-model assumptions diagnostic

#### Is it possible to deal with datasets of graphs with different number of nodes in graph nural networks?

**Source:** stats**Views:** 4**Score:** 2**Tags:** machine-learning neural-networks graph-neural-network