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Problems using integral function in Matlab

  1. Jan 11, 2013 #1
    Hi there!

    i have this function handle:

    integrando= @(x,landa,t) 1-exp(-((1/(landa*t))*((exp(-landa*x)/x)+((x-x0).*(1+landa*x0)-x0)*(exp(-landa*x0)/(x0^2)))));

    which as you can see using

    fplot(@(x) integrando(x,3,0.00063),[0 1.1225])

    its value is constant (actually 1, and then starts decreasing exponentially until drops to zero at 1.1225). Landa and t are parameters that change the curvature of this drop. Since this is a positive and finite function, I'm waiting a positive integral. However, integrating this same function on this same interval, I get negative figures!

    >> q1=integral(@(x) integrando(x,3,0.00063),0,1.1225)

    q1 =

    -20.3981



    This is getting me nuts! I would very much appreciate any help. Thanks in advance!
     
  2. jcsd
  3. Jan 11, 2013 #2

    kreil

    User Avatar
    Gold Member

    What value are you using for x0?

    I used 2 just to see if the code works, and I got:

    integrando= @(x,landa,t) 1-exp(-((1/(landa*t))*((exp(-landa*x)/x)+((x-2).*(1+landa*2)-2)*(exp(-landa*2)/(2^2)))));

    fplot(@(x) integrando(x,3,0.00063),[0 1.1225])

    q1=integral(@(x) integrando(x,3,0.00063),0,1.1225)

    q1 =

    1.1225
     
  4. Jan 12, 2013 #3
    hi kreil,

    I'm using x0=1.1225 ,which is the same value as the limit of integration. If you try again using that value on 'integrando', you'll see the result of the integral is a negative number which doesn't make any sense to me
     
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