if (iTimeIndex > 0 || prevHiddenUnitActivation != null) {
                    //Note that prevHiddenUnitActivation may be non-null at t=0 for TBPTT
                    Nd4j.gemm(deltaifogNext, inputWeights, epsilonNextSlice, false, true, 1.0, 1.0);
                } else {
                    //No contribution from forget gate at t=0