lodin is computing the cosine directly (note cos 0 = 1 -> "same sign" while cos 180 degrees = -1 -> "opposite sign").

Maybe this is what you mean, but I don't actually calculate the angle (or cosine) between $_[0] and $_[1]. I calculate the respective angles of $_[0] and $_[1] against the positive axis, and compare them.

Equivalently, you could also view it as I'm taking the norm of the two 1D vectors $_[0] and $_[1], which gives me two unit vectors pointing in the direction of $_[0] and $_[1], which I then test for equality. If they're equal, they point in the same direction, and in 1D that means they have the same sign.

lodin

In reply to Re^3: Seeing if two numbers have the same sign ($x / abs $x) by lodin
in thread Seeing if two numbers have the same sign by grinder

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.