Let $\mathcal{P}$ be the set of vectors defined by
\[\mathcal{P} = \left\{\begin{pmatrix} a \\ b \end{pmatrix} \, \middle\vert \, 0 \le a \le 2, 0 \le b \le 100, \, \text{and} \, a, b \in \mathbb{Z}\right\}.\]
Find all $\mathbf{v} \in \mathcal{P}$ such that the set $\mathcal{P}\setminus\{\mathbf{v}\}$ obtained by omitting vector $\mathbf{v}$ from $\mathcal{P}$ can be partitioned into two sets of equal size and equal sum.
1. **Define the set $\mathcal{P}$**:
   \[
   \mathcal{P} = \left\{\begin{pmatrix} a \\ b \end{pmatrix} \, \middle\vert \, 0 \le a \le 2, 0 \le b \le 100, \, \text{and} \, a, b \in \mathbb{Z}\right\}
   \]
   This set contains all vectors with integer coordinates where \(a\) ranges from 0 to 2 and \(b\) ranges from 0 to 100.

2. **Count the total number of vectors in $\mathcal{P}$**:
   \[
   \text{Total number of vectors} = 3 \times 101 = 303
   \]
   This is because there are 3 possible values for \(a\) and 101 possible values for \(b\).

3. **Condition for partitioning $\mathcal{P} \setminus \{\mathbf{v}\}$**:
   We need to find a vector \(\mathbf{v}\) such that removing it from \(\mathcal{P}\) allows the remaining 302 vectors to be partitioned into two sets of equal size and equal sum.

4. **Sum of all vectors in $\mathcal{P}$**:
   \[
   \sum_{\mathbf{v} \in \mathcal{P}} \mathbf{v} = \sum_{a=0}^{2} \sum_{b=0}^{100} \begin{pmatrix} a \\ b \end{pmatrix}
   \]
   Calculate the sum of the coordinates separately:
   \[
   \sum_{a=0}^{2} \sum_{b=0}^{100} a = 101 \sum_{a=0}^{2} a = 101 \times 3 = 303
   \]
   \[
   \sum_{a=0}^{2} \sum_{b=0}^{100} b = 3 \sum_{b=0}^{100} b = 3 \times \frac{100 \times 101}{2} = 3 \times 5050 = 15150
   \]
   Therefore,
   \[
   \sum_{\mathbf{v} \in \mathcal{P}} \mathbf{v} = \begin{pmatrix} 303 \\ 15150 \end{pmatrix}
   \]

5. **Sum of the remaining vectors**:
   After removing \(\mathbf{v} = \begin{pmatrix} a \\ b \end{pmatrix}\), the sum of the remaining vectors is:
   \[
   \sum_{\mathbf{v} \in \mathcal{P} \setminus \{\mathbf{v}\}} \mathbf{v} = \begin{pmatrix} 303 - a \\ 15150 - b \end{pmatrix}
   \]
   For the remaining vectors to be partitioned into two sets of equal size and equal sum, both coordinates of the sum must be even:
   \[
   303 - a \text{ must be even}
   \]
   \[
   15150 - b \text{ must be even}
   \]

6. **Determine the values of \(a\) and \(b\)**:
   \[
   303 - a \text{ is even} \implies a \text{ is odd}
   \]
   \[
   15150 - b \text{ is even} \implies b \text{ is even}
   \]
   Since \(a\) can only be 0, 1, or 2, the only odd value is 1. Therefore, \(a = 1\). \(b\) must be an even number between 0 and 100.

7. **Conclusion**:
   The vectors \(\mathbf{v}\) that satisfy the condition are of the form:
   \[
   \mathbf{v} = \begin{pmatrix} 1 \\ 2n \end{pmatrix} \quad \text{for} \quad n \in \{0, 1, 2, \ldots, 50\}
   \]

The final answer is \( \boxed{ \left\{\begin{pmatrix} 1 \\ 2n \end{pmatrix} \, \middle\vert \, n \in \{0, 1, 2, \ldots, 50\}\right\} } \)