"PaddlePaddle: From Beginner to 'Alchemy Master' (2) - Calculating 1+1"

This chapter introduces how to perform simple tensor operations and variable operations using the PaddlePaddle Fluid version. First, two constant tensors x1 and x2 with shape [2, 2] and value 1 are defined using the `fill_constant()` function, and then their sum is calculated using the `sum()` function. Next, a CPU executor is created and parameters are initialized, finally outputting the result [[2, 2], [2, 2]]. Then, it demonstrates how to perform operations using variables, which is defined in `variable_sum.py`.