أحمد مهدي صالح. “Development of a Reduced Estimator to Estimate the Variance and Covariance Matrix With Large Dimensions Using Hyperbolic Trigonometric Functions - (Chemical Properties of the Soil of the Tigris Basin in Wasit Governorate)”. Iraqi Journal for Administrative Sciences, vol. 13, no. 52, Nov. 2024, pp. 227-45, https://mail.journals.uokerbala.edu.iq/index.php/ijas/article/view/2653.