Dimension mismatch when using SPMe model to calculate Ohmic heat

[xingxie123]

When I used the default SPMe model to calculate heat generation, one component of the Ohmic heat is calculated in the following way: Q_ohm_s_n = -pybamm.inner(i_s_n, pybamm.grad(phi_s_n)). Using default var_pts, the shape of i_s_n is (20,100), and the shape of grad(phi_s_n) is (21,100). It is supposed to encounter shape mismatch error but the program runs perfectly fine.
However, when I try to modify basic_SPM.py to basic_SPMe.py, I use the same code to calculate Ohmic heat but it returns dimension mismatch error. How should I go about resolving this?