Notices
Results 1 to 9 of 9

Thread: Help to understand one simple function

  1. #1 Help to understand one simple function 
    New Member
    Join Date
    Sep 2013
    Posts
    2
    please, can you help me to understand following formula (my math is a bit rusty,....)

    I have a following function: where n=2 and −5.0 ≤ xi 5.0

    f (x) = n x2i
    i=1

    So, my question is: since n=2 does it mean that the function needs 2 numbers on input, or just one? I think that only one, is it correct? For example if I use for x number 1 I will get f(x) = 2? And for x=2 I will get f(x) = 8?

    thanks,
    m.


    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Freshman
    Join Date
    Jan 2013
    Posts
    34
    Yes, "n= 2" means that i takes on the values "1" and "2". That "summation form" can be used to write very long sums simply, but with only two terms, it just gets in the way!
    That is just requiring two input numbers, and . They are NOT necessarily the same.


    Reply With Quote  
     

  4. #3  
    New Member
    Join Date
    Sep 2013
    Posts
    2
    Quote Originally Posted by HallsofIvy View Post
    Yes, "n= 2" means that i takes on the values "1" and "2". That "summation form" can be used to write very long sums simply, but with only two terms, it just gets in the way!
    That is just requiring two input numbers, and . They are NOT necessarily the same.
    many thanks
    Reply With Quote  
     

  5. #4  
    Forum Junior
    Join Date
    Sep 2010
    Location
    92
    Posts
    217
    Quote Originally Posted by miro View Post
    please, can you help me to understand following formula (my math is a bit rusty,....)

    I have a following function: where n=2 and −5.0 ≤ xi 5.0

    f (x) = n x2i
    i=1

    So, my question is: since n=2 does it mean that the function needs 2 numbers on input, or just one? I think that only one, is it correct? For example if I use for x number 1 I will get f(x) = 2? And for x=2 I will get f(x) = 8?

    thanks,
    m.
    Your summation is simply a function f(x) = x12 + x22 where x1 and x2 are values in the interval -5 ≤ xi ≤ 5. Are you sure you posted the correct summation? What are you trying to accomplish? You can arbitrarily choose any two numbers in the interval and add their squares.

    Jagella
    Reply With Quote  
     

  6. #5  
    Bassaricyon neblina Olinguito's Avatar
    Join Date
    Aug 2013
    Location
    Greater London, England, UK
    Posts
    45
    The function is a plot of the paraboloid surface for .
    Reply With Quote  
     

  7. #6  
    Forum Junior
    Join Date
    Sep 2010
    Location
    92
    Posts
    217
    Quote Originally Posted by Olinguito View Post
    The function is a plot of the paraboloid surface for .
    But there's only one variable, x.

    Jagella
    Reply With Quote  
     

  8. #7  
    Bassaricyon neblina Olinguito's Avatar
    Join Date
    Aug 2013
    Location
    Greater London, England, UK
    Posts
    45
    There are two independent variables, and , and . Thus .

    Alternatively, where .
    Last edited by Olinguito; September 13th, 2013 at 07:43 AM.
    Reply With Quote  
     

  9. #8  
    Forum Junior
    Join Date
    Sep 2010
    Location
    92
    Posts
    217
    Quote Originally Posted by Olinguito View Post
    There are two independent variables, and , and . Thus .

    Alternatively, where .
    Thanks, but what happened to the variable, y? You stated earlier that z = x2 + y2.

    Jagella
    Reply With Quote  
     

  10. #9  
    Bassaricyon neblina Olinguito's Avatar
    Join Date
    Aug 2013
    Location
    Greater London, England, UK
    Posts
    45
    Sorry, clash of notation. The OP used to represent a point in whereas I used for such a point. The two represent different variables.

    NB: The OP only wrote and did not actually say the variable was. I’m assuming because it’s seems to me the most logical assumption to make.
    Last edited by Olinguito; September 15th, 2013 at 06:19 AM.
    Reply With Quote  
     

Similar Threads

  1. Replies: 0
    Last Post: May 30th, 2012, 03:05 PM
  2. Help Me Understand
    By Callie in forum Computer Science
    Replies: 13
    Last Post: December 29th, 2011, 07:45 PM
  3. How to understand this?
    By kowalskil in forum Politics
    Replies: 6
    Last Post: July 8th, 2011, 12:00 AM
  4. Please read. If you understand it, you'll understand YOU
    By Shannon in forum General Discussion
    Replies: 24
    Last Post: June 2nd, 2010, 11:27 PM
  5. Help me understand Knuth
    By xsive in forum Computer Science
    Replies: 0
    Last Post: May 12th, 2008, 01:37 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •