索引超出了数组的边界

当我尝试运行应用程序时，它在float[] u_f = a[userid];行显示Index was outside the bounds of the array任何想法?另外，用户ID可以是任何整数，但我取整数的索引，取值范围在(item为0,1143600)和(user为0,89395)之间，并以此为基础进行计算。然后，我的计算是基于存储在数组a中的userid值的索引，而不是基于userid的值。提前感谢

        float[][] a = Enumerable.Range(0, 89395).Select(i => new float[100]).ToArray();
        float[][] b = Enumerable.Range(0, 1143600).Select(j => new float[100]).ToArray();
        int[] c = new int[1258038];
        int[] d = new int [92160];
        ........
        public float dotproduct(int userid, int itemid)
        {
            result = 0f;
            float[] u_f = a[userid];   //  <----Error Line (index was outside the bounds of array)
            float[] i_f = b[itemid];
            for (int i = 0; i < u_f.Length; i++)
            {
                result += u_f[i] * i_f[i];
            }
            return result;
        }
        private void btn_recomm_Click(object sender, EventArgs e)
        {
            if (!String.IsNullOrEmpty(txtbx_id.Text) && String.IsNullOrEmpty(txtbx_itemid.Text) && !String.IsNullOrEmpty(txtbx_noofrecomm.Text))
            {
                    int sc = Convert.ToInt32(txtbx_id.Text);
                    int n = Convert.ToInt32(txtbx_noofrecomm.Text);
                    int userseq=Array.IndexOf(d, sc);
                    var results = new List<float>(1143600);
                    for (int z = 0; z <= 1143600; z++)
                    {
                        results.Add(dotproduct(userseq, z));
                    }
                    var sb1 = new StringBuilder();
                    foreach (var resultwithindex in results.Select((r, index) => new { result = r, Index = index }).OrderByDescending(r => r.result).Take(n))
                    {
                        sb1.AppendFormat("{0}: {1}", d[resultwithindex.Index], resultwithindex.result);
                        sb1.AppendLine();
                    }
                    MessageBox.Show(sb1.ToString());

            }
            if (!String.IsNullOrEmpty(txtbx_id.Text) && !String.IsNullOrEmpty(txtbx_itemid.Text) && String.IsNullOrEmpty(txtbx_noofrecomm.Text))
            {
                int uid = Convert.ToInt32(txtbx_id.Text);
                int iid = Convert.ToInt32(txtbx_itemid.Text);
                int userseq0 = Array.IndexOf(d, uid);
                int itemseq0 = Array.IndexOf(c, iid);
                dotproduct(userseq0, itemseq0);
                MessageBox.Show("The Score of item id " + itemseq0 + " is " + result);
            }