+ Reply to Thread
Results 1 to 5 of 5

Thread: Open endpoints on segments and rays

  1. #1

    Open endpoints on segments and rays

    Its not really a contruction question...

    I want to create an open circle for an endpoint. This would seem logical to be in the point style sub-menu but its not there. I've tried constructing very small circles but this doesn't really work. I've also searched for an answer but no luck.

    I'm doing a unit on domain and range and want to include "x is strictly greater/less than..." but without an option for an open circle I don't see how to do it.

    Help would be appreciated. Thank you.

  2. #2
    Hi,

    You can choose large points and use white for the interior color; then they will look like open circles. See the attached sketch. Others may have a better suggestion...

    Elizabeth
    Attached Files

  3. #3
    Sketchpad Developer
    Join Date
    Oct 2010
    Location
    Philadelphia
    Posts
    71
    PapaG, Elizabeth's answer is exactly right. Of course, you can choose any point size (except Dot) that's appropriate to the images of domain and range you want to present in your sketch. You should also be aware that any point you create on the segment or ray will not fit the "strictly greater/less than" paradigm, because you can always drag a point all the way to the endpoint. The best you can do is simulate this by putting the endpoints a small distance away from the limit. (You also need to be aware of the fact that both the screen and your mouse or other pointing device are discrete devices; for instance, the mouse always moves by 1 pixel at a time.)

    There's one other thing worth mentioning, if you're making a number of such segments (or rays). You can make an Open Interval custom tool by creating a segment with white endpoints of your favorite size, selecting the segment and endpoints, and creating a custom tool. Any time you use the resulting custom tool, you'll get the same line style and point style as the original from which you made the tool. If you're making a lot of "open interval" segments like this, the tool can save time because you'll automatically get a segment just like the one you used to make the tool.

    --Scott

  4. #4
    Elizabeth, thanks for your idea. It works well enough.

    SCOTT! Glad to hear from a developer.

    Though your comment about the limitation of these endpoints fitting "the "strictly greater/less than paradigm" is completely unnecessary. First its a bit insulting to for you to tell me that I "need to be aware...". Thank you, I am aware. Second, the idea of the mouse being a discrete device is also painfully obvious. Third, the use of open/closed circles is a universally accepted convention and taught across the world. When posing the question I did not feel the need to clarify to such a degree.

    The entire Sketchpad program requires you to accept these limitations, given that a point has neither volume, area or length.

    Regardless, Elizabeth's idea, though clever, is hardly the answer I am looking for. It would seem easy enough to add an option into the point style drop down menu to include open circles. This would also come in handy when talking about piecewise functions or removable discontinuities. I am sure educators at all levels would find it useful.

    I guess I am wondering if I could make this suggestion: Add an option to the POINT STYLE sub-menu that offers an open circle. It seems simple enough and we could certainly use it!

  5. #5
    Sketchpad Developer
    Join Date
    Oct 2010
    Location
    Philadelphia
    Posts
    71
    I apologize, PapaG, I had no intention of insulting you. (When I post on this forum, I try to explain myself as completely as possible, since a wide variety of users may be perusing this thread. But I regret having expressed myself in a way that sounded so condescending.)

    You say that using a white point "is hardly the answer I am looking for." Can you describe in what way a white point is inadequate for the purpose of displaying an open circle? Is the problem that white is not one of the immediately-available colors on the Display | Color submenu? If so, I recommend using Advanced Preferences to edit the color menu and replace one of the less-useful colors with white. And if not, I'd appreciate knowing in more detail why Elizabeth's answer is inadequate.
    Thanks,
    Scott

+ Reply to Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts