GLSharp.Util.Matrix4X4.MakeFrustrum C# (CSharp) Method

        public static Matrix4X4 MakeFrustrum(float left, float right, float bottom, float top, float znear, float zfar)
        {
            Matrix4X4 ret = new Matrix4X4(null);

            float rl = (right - left);
            float tb = (top - bottom);
            float fn = (zfar - znear);
            ret.Elements[0] = (znear * 2) / rl;
            ret.Elements[1] = 0;
            ret.Elements[2] = 0;
            ret.Elements[3] = 0;
            ret.Elements[4] = 0;
            ret.Elements[5] = (znear * 2) / tb;
            ret.Elements[6] = 0;
            ret.Elements[7] = 0;
            ret.Elements[8] = (right + left) / rl;
            ret.Elements[9] = (top + bottom) / tb;
            ret.Elements[10] = -(zfar + znear) / fn;
            ret.Elements[11] = -1;
            ret.Elements[12] = 0;
            ret.Elements[13] = 0;
            ret.Elements[14] = -(zfar * znear * 2) / fn;
            ret.Elements[15] = 0;

            return ret;
        }