some typos cause "variables not found": samples_result/samples_reuslt, dirs/viewdirs
gradient and backward cannot reach two nn.Parametersh_fields and density_fields since torch.cat((self.sh_fields, self.density_fields), dim=3). The proper way is to use them separately
samples_result/samples_reuslt,dirs/viewdirsnn.Parametersh_fieldsanddensity_fieldssincetorch.cat((self.sh_fields, self.density_fields), dim=3). The proper way is to use them separatelytrilinear_interpolationseems wrong, fixed