<div dir="ltr"><div dir="ltr"><span style="text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:24px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;display:inline;white-space:pre-wrap;float:none;background-color:transparent">Dear sir<br>Thanks for your reply, but I still don't understand why  the value of <span style="text-align:left;color:rgb(51,51,51);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:16px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;display:inline;white-space:normal;float:none;background-color:transparent">the cutoff distance </span>is 4.4 <span style="text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:24px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;display:inline;white-space:pre-wrap;float:none;background-color:transparent">in tutorial 14</span>.<br><span style="text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:24px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;display:inline;white-space:pre-wrap;float:none;background-color:transparent">Can you elaborate on it?<br><br>Thank for your help!<br><br>___________________________________________________<br><span title="" style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap">Kaifang Qu</span><br style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap"><span title="" style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap">School of Electronics and Optical Engineering</span><br style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap"><span title="" style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap">Nanjing University of Posts and Telecommunications</span><br style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap"><span title="" style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap">Nanjing</span><br style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap"><span title="" style="background:none;text-align:left;color:rgba(0,0,0,0.87);text-transform:none;text-indent:0px;letter-spacing:normal;font-size:18px;font-style:normal;font-variant:normal;font-weight:400;text-decoration:none;word-spacing:0px;white-space:pre-wrap">China</span></span><b></b><i></i><u></u><strike></strike><br></span><b style="font:700 13.33px/19.99px Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent"></b><i style="font:italic 400 13.33px/19.99px Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent"></i><u style="font:400 13.33px/19.99px Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:underline;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent"></u><sub style="font:400 9.2px/13.8px Arial,Helvetica,sans-serif;text-align:left;c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