<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Sun, Oct 4, 2015 at 9:18 AM, Bill Cox <span dir="ltr"><<a href="mailto:waywardgeek@gmail.com" target="_blank">waywardgeek@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra">Edwards form:<br></div><div class="gmail_extra"><br></div><div class="gmail_extra"><div style="font-size:12.8000001907349px">    sn3 = (sn1(cn2/dn2) + sn2)/(1 + d*sn1(cn1/sn1)sn2(cn2/dn2)</div><div style="font-size:12.8000001907349px">    cn3/dn3 = ((cn1/dn1)(cn2/dn2) - sn1*sn2)/(1 - d*sn1(cn1/dn1)sn2(cn2/dn2))</div></div></div></blockquote><div><br></div><div>I left out one factor.  The Edwards form of the ellipse point addition law is:</div><div><br></div><div><div>    sn3 = (sn1(cn2/dn2) + sn2(cn1/dn1))/(1 + d*sn1(cn1/sn1)sn2(cn2/dn2)</div><div>    cn3/dn3 = ((cn1/dn1)(cn2/dn2) - sn1*sn2)/(1 - d*sn1(cn1/sn1)sn2(cn2/dn2)</div></div><div><br></div><div>Bill</div></div></div></div>