Mac OS X Grapher

Discussion in 'Mac Apps and Mac App Store' started by iDavidLeeRoth, Feb 20, 2007.

  1. iDavidLeeRoth macrumors regular

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    Sep 4, 2006
    #1
    Is it possible to graph a log that isn't to the base 10 with the Mac OS X Grapher? If not, do you know of an application hat has this feature?
     
  2. bearbo macrumors 68000

    bearbo

    Joined:
    Jul 20, 2006
    #2
    i'll check grapher, but i'm sure excel can do it. do you know how to do that?

    why do you want to graph non-base-10 log graphs?
     
  3. swiftaw macrumors 603

    swiftaw

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    Jan 31, 2005
    Location:
    Omaha, NE, USA
  4. bearbo macrumors 68000

    bearbo

    Joined:
    Jul 20, 2006
    #4
    do you know what a log-log graph is?

    now, how did you propose to use the equation you provided to graph a base-2 log-log graph?
     
  5. iDavidLeeRoth thread starter macrumors regular

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    Sep 4, 2006
    #5
    I'm trying to graph log(base5)x.

    I know how to do it manually, but I'd like to have a nice pretty graph :)
     
  6. swiftaw macrumors 603

    swiftaw

    Joined:
    Jan 31, 2005
    Location:
    Omaha, NE, USA
    #6
    Oops, I misread what he wanted.

    So suppose you want to plot the log of base a.

    then log_a x can be expressed as ln x / ln a

    where ln is the natural log

    so in grapher, plotting y = ln x / ln a will give you a plot of log_a x for some constant a

    y = ln x / ln 5
     
  7. iDavidLeeRoth thread starter macrumors regular

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    Sep 4, 2006
    #7
    ***** genious! Thanks!
     
  8. bearbo macrumors 68000

    bearbo

    Joined:
    Jul 20, 2006
    #8
    but how do you do that in grapher properly, with the correct label and stuff?

    i mean, i know excel can do that easily.
     
  9. swiftaw macrumors 603

    swiftaw

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    Jan 31, 2005
    Location:
    Omaha, NE, USA
    #9
    No problem

    Wasn't doing a log-log graph, I was using linear axes
     
  10. iDavidLeeRoth thread starter macrumors regular

    Joined:
    Sep 4, 2006
    #10
    Oh, one last thing....

    How do I go to a specific point on a graph.


    Let's say I really want to go to X=5000 on the graph to see its Y intersection....

    Is there a "Table" like function that comes on TI-calcs?
     
  11. swiftaw macrumors 603

    swiftaw

    Joined:
    Jan 31, 2005
    Location:
    Omaha, NE, USA
    #11
    No idea, never used grapher. I was just giving the OP a way to express log base 5 in terms on natural log functions so he could plot it.

    Equation->Evaluation
     
  12. bearbo macrumors 68000

    bearbo

    Joined:
    Jul 20, 2006
    #12
    yes there is table for ti-83, 84, 86, 89... i wouldn't bother with it thought if i were you.
     
  13. iDavidLeeRoth thread starter macrumors regular

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    Sep 4, 2006
    #13
    Dude, you are a lifesaver!

    Grapher is SO powerful...
     
  14. swiftaw macrumors 603

    swiftaw

    Joined:
    Jan 31, 2005
    Location:
    Omaha, NE, USA
    #14
    Yeah, I've never played with it before but just looking at it now it seems pretty useful.
     
  15. iDavidLeeRoth thread starter macrumors regular

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    Sep 4, 2006
    #15
    Is there a way to go to the intersection point of two graphs?:confused:

    Edit: Nevermind. Coming from Windows, I'm not used to exceptional documentation built right into the app.
    Finding the intersection of two curves
    You can find the points at which two equations intersect.


    Select two equations, and choose Equation > Find Intersection. Then do one of the following:


    To find the intersection nearest a point on an axis, enter that location in the text field beside the axis name and press Return.

    To find the intersection nearest any point in the graph, click that point.

    The intersection is displayed on the graph. You can change the color of the cross-hairs by clicking the color well.

    To select two equations, click the first one in the Equations list, and then Shift-click the second one.


    See also
    Analyzing graphs

    Edit: actually, something is screwing up. I am trying to find out where y=4565 and y=6^x intersect on a chart. When I try to find the intersection, I get this:


    [​IMG]

    I know how to solve it by hand using logs, but the purpose of the exercise is to be able to show that we know how to do it on the graphs.
     
  16. iDavidLeeRoth thread starter macrumors regular

    Joined:
    Sep 4, 2006
    #16
    So, does anyone know why I can't find the intersection?

    Also, my grapher no longer wants to export to latex :(
     
  17. mickclns macrumors newbie

    Joined:
    Feb 27, 2008
    #17
    It would really be nice to be able to do a subscript such as for a log. Something analogous to 3^5 to do 3 to the fifth power. I don't know that it is not possible but I haven't found it. Is there anyone from Apple who listens to this forum?

    Anyway, for those others out there asking about this, I see 3 ways to kludge it to get the graph of, say, y = log base 7 of x:
    y= log(x) / log(7)
    y = ln(x) / ln(7)
    x = 7^y

    Of course, it would be nice to have it prettyprinted as we would like to see it.
     
  18. anonamac macrumors newbie

    Joined:
    Jan 3, 2012
    #18
    hey guys, graphing logs that are not base 10 is easy: for example i had to graph Log(base 3/2) (x) instead of trying log^(3/2) (x) and getting a syntax error, put the base BEFORE the log and it will graph it so it becomes 3/2Log(x) :D Tell me if this helps :D
     
  19. mickclns macrumors newbie

    Joined:
    Feb 27, 2008
    #19
    anonomac, You're right, it is easy, but the object is to first get it right, then get it easy. Read my post above. If you don't understand get out an intermediate / college algebra or precalculus book. What you've graphed is
    y = 3/2 times log x which is not the same as y = log (base 3/2) of x.

    It (mine above) uses the change-of-base formula.

    The idea is that (changing the base from b to c) you change the base but divide by the log (new base) of the old base. That is,
    log base b of a =(log base c of a) /(log base c of b).
    log x means log base 10 of x and
    ln x means log base e of x (where e = 2.71........ )

    So, log base 7 of x = log x / log 7 = ln x / ln 7 =
    log base 134 of 7 / log base 134 of 7

    In the above, the base 7 is changed first to 10, then to e, then to 134, all of them yielding the same answer as the original (whether using for graphing or any other mathematical use).

    BTW, you need to do the same thing in your scientific / graphing calculator to get an accurate graph or calculation that involves a log to a base other than 10 or e . In my TI-89, I don't even have a log button so I have to use ln for everything (there is a function for programming which I can use for any meaningful base).

    Anyway, I hope this helps clear the fog.
     
  20. mickclns macrumors newbie

    Joined:
    Feb 27, 2008
    #20
    reply to eqn intersections #14

    iDLR, (sorry, #15, not #14)
    I used your two equations and got an intersection of
    x = 4.7029
    y = (of course) 4565.

    Before I used Find Intersection, I zoomed out a bunch of times until I could see the horizontal line, the changed View - Frame Limits so y stayed the same and x went from 0 to 10. I could clearly see the intersection and the menu worked just fine.

    Sorry for the answer 5 years late (wonder if you'll see this).
     

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