as how in the image blow,
the shape of the col_buffer_ is (kernel_dim_G)(HoWo) ,where Ho、Wo is the spatial dim of the top bolob, however,
after useing conv_im2col_cpu(), only size of kernel_dim(HoWo) are assigned a value, the left (kernel_dim_(G-1))(HoWo) memory is not assigned.
