Abstract: A computing method, suitable for computing a transformer model, include following steps. An input matrix corresponding to an input sequence of feature vectors is projected into a query matrix according to first learnable weights. The input matrix is projected into a value matrix according to second learnable weights. A factorized matrix is generated by an incomplete Cholesky factorization according to the query matrix and a transpose of the query matrix. An intermediate matrix is calculated according to a product between a transpose of the factorized matrix and the value matrix. An output matrix is calculated according to a product between the factorized matrix (H) and the intermediate matrix.