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Basic matlab help with plotting

  1. Aug 4, 2011 #1

    I am trying to write a short matlab program that plots concentration vs distance (oxygen sag curve from two different bod sources in a river). I know the equation im using is:

    C= Cs - [(kd*Mo)*(exp(-x*kr/u)-exp(-x*ka/u))/(Q*ka-kr)] - (Cs-Co)*exp(-x*ka/u) - [(kd*Mo)*(exp(-(x-L)*kr/u)-exp(-(x-L)*ka/u))/(Q*ka-kr)].

    Its very long and im having trouble getting it to work in matlab form.
    Can someone used to matlab give me some hints how to make this work?

    I know how to execute a plot by plot(x,C) but the equation is giving me trouble.

    Any help would be greatly appreciated.
  2. jcsd
  3. Aug 4, 2011 #2


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    Homework Helper

    I'm going to assume everything in there except x is a constant. First, you have to specify what points you want to use for x. For example, you could do:

    x = linspace(0,1,100)

    In a nutshell, this defines x as 100 points between 0 and 1. After this, you can type:

    C= Cs - [(kd*Mo)*(exp(-x*kr/u)-exp(-x*ka/u))/(Q*ka-kr)] - (Cs-Co)*exp(-x*ka/u) - [(kd*Mo)*(exp(-(x-L)*kr/u)-exp(-(x-L)*ka/u))/(Q*ka-kr)]


    If that still doesn't work, I don't know. Without knowing what all of these letters are, it's close to impossible to debug what you're doing.
  4. Aug 5, 2011 #3
    thanks, i got it working, just needed to correct some bracketing.
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