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Matlab function HW help please

  1. Nov 6, 2005 #1
    Hi, i need to write function for the following.
    W=k1x if x<d
    W=k1x+2k2(x-d) if x>=d

    Question is: Create function that computes distance x using the input parameters W, k1, k2, and d.
    k1=10^4
    k2=1.5*10^4
    d=0.1
    W=500 and 2000
    so i get the formulas solving for x that are
    x=W/k1 and x=(W+2k2d)/(k2+2k2)
    but I dont know how to solve for x as I get error which says that x is not defined when i use if/else and i tried using for loop and got the same problem.
    here is my code:
    function x = spring (W)
    k1=10^4;
    k2=1.5*10^4;
    d=0.1;
    if x < 0.1
    x=W/k1
    else x >= 0.1
    x=(W+(2*k2)*d)/(k1+(2*k2))
    end

    Any help please?
     
  2. jcsd
  3. Nov 6, 2005 #2
    Hi,
    I see the problem not with the code but with the concept of this calculation it self. If you took a look on what you have written it's obvious why doesn't it work.
    How can you evaluate a function depending on the output of the function?
    you say for example
    y = 3 * x if y < 5
    y = 5 * x + 7 if y >= 5
    this conditions can't be on the dependent variable it can only be on the independent variable you can calculate it easily.
    so y = 3 * x if x < 5/3
    and y = 5 * x + 7 if x >= -2/5

    I know that's are not mutual exclusive conditions. Which in fact what you are doing in first place?

    but why matlab say this error?
    review the code:
    Code (Text):

    function x = spring (W)
    k1=10^4;
    k2=1.5*10^4;
    d=0.1;
    if x < 0.1
     
    see untill this comparison you haven't made any evaluation for the x.
    If your calculation are recurrsive - depend on the previous value of x -, then you can assume an inital value for x to make this comparison

    That's all,
    bye
     
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