[bn layer] derivative of deviation

[lhs8928]

When it comes to think of the derivative of deviation(2) there are 2 incoming derivative. One from the variance(3) and the other from intermediate output(5). These 2 incoming derivative should be merged and the be averaged. But current implementation averaged the derivative from intermediate output(5) and then subtract(merge) the other(derivative from variance). I think this might leads to different result.

Please check following diagram.

(1) input (2) deviation (3) variance (4) inv_std
(5) intermediate output (6) gamma (7) beta (8) output

[taos-ci]

:octocat: cibot: Thank you for posting issue #1977. The person in charge will reply soon.