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DOUBT in numerical integration

  1. Nov 18, 2011 #1
    I have doubt in MATLAB

    How to integrate

    exp(x)*erfc(x) ? in MATLAB

    The warning msg it is displaying is :

    EXPLICIT integral could not be found
     
  2. jcsd
  3. Nov 19, 2011 #2
    Are you trying to do numerical or symbolic integration? Maybe that's a function which has no analytic integral? If numerical, what are the limits?
     
  4. Nov 19, 2011 #3
    I have an expression involving seven parameters. I need to first integrate the entire expression from 0 to t and then get the values by substitution method. Matlab is not supporting symbolic integration. hence I am planning to Numerical .
     
  5. Nov 19, 2011 #4
    Oops I didn't see the title of you message. In that case there must be something wrong with your Matlab code since it should be able to integrate anything it can evaluate. Could you paste the code, including the limits of the integration?

    Seems like a function that can easily be numerically integrated over any range of x.

    Does it actually produce a solution, but you don't trust it because of the warning message?
     
  6. Dec 7, 2011 #5
    e^(a+bt) erfc(-c+rt)exp((t-q)/l)

    within the limits o to t
     
  7. Dec 8, 2011 #6

    MATLABdude

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    If you're using undefined a, b, c, r, q, and l, that's not numerical integration (especially if you're also attempting to integrate to an undefined 't').
     
  8. Dec 8, 2011 #7
    I have all the values of a, b, c, r, q, l and t. Then how to go about it ?
     
  9. Dec 8, 2011 #8

    MATLABdude

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    Write a small script to do so. For instance, the following uses the trapezoid rule to find the integral between 0 and pi of the sine function.

    Code (Text):

        t=0:pi/100:pi;  % t values
        y=sin(1*t);     % calculation of function at all t
        A = trapz(y,t); % implements trapezoid rule
     
    Why did I explicitly use 1*t? While I could have just used t, it's to illustrate that there is no implicit multiplication in MATLAB (i.e. rt refers to the value / vector / matrix rt, while r*t refers to the product of r and t). I'd suggest writing up a small function (just as I've done above) in Notepad / Text Editor / EMacs / Vi, and then paste it here between the [code ][/ code] tags (no spaces in the tags).
     
  10. Dec 8, 2011 #9
    I will get back to you sir.
     
  11. Dec 8, 2011 #10
    I will clear one doubt. rt is r*t only. rt is definitely not a single variable.

    I have one doubt cant we take some fictitous value and start integration of error function and exponential ?
     
  12. Dec 11, 2011 #11

    MATLABdude

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    It's your work--you can put in whatever you want!
     
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