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Matlab graph

  1. Jul 28, 2011 #1
    Dear fellows
    I need to draw a graph of a complex function in matlab, but could not do so, can you please help me in this issue??
    I have mentioned each and every constant required for function(complex function),
    y1=1.9417+3.5012i;
    y2=1.9417+3.5012i;
    y3=4.7348-1.4837;
    y4=4.7345+1.4837;
    y5=202.701;
    M1=1.558*10^12-1.90339*10^12i;
    M2=1.536*10^12+1.8116*10^12;
    M3=-6.0446*10^11+4.0463*10^12i;
    M4=-4.134*10^11-3.954*10^12i;
    M5=-2.674*10^8-1.222*10^8i;
    a=1;
    O1=0.023475-0.0252192i;
    O2=0.023475+0.0252192i;
    O3=-0.0225775-0.0197677i;
    O4=-0.0225775+0.0197677i;
    O5=-0.000015578;
    w=2;
    t=0.1;
    z=1;
    J=(1i*a*O1-y1)*M1*Exp(-y1*x)+(1i*a*O2-y2)*M2*Exp(-y2*x)+(1i*a*O3-y3)*M3*Exp(-y3*x)+(1i*a*O4-y4)*M4*Exp(-y4*x)+(1i*a*O5-y5)*M5*Exp(-y5*x);
    U=J*Exp(wt+iaz);
    x=linspace(0,5);
    plot(x,Re(U))

    Any kind of help will be appreciated,

    Thanks
     
  2. jcsd
  3. Jul 28, 2011 #2
    I don't use matlab, but I will point out a couple of things in your post which may or may not be in your actual matlab script (did you copy and paste or re-typed?).

    y3 and y4 seem to have the i missing in the second term
    you do not have proper matlab function declared, it seems you are trying to plot a variable, not a function (I know what you mean though, but let's be proper).
    you define the variable x AFTER you use it to create J, maybe if you would move the line "x=linspace(0,5); " up a couple of rows, things will work?
     
  4. Jul 28, 2011 #3
    I copied it from the matlab "m-file", the values of y1,2,3,4,5 are constants may be complex may be real,
    the function to plot is (real part of "u" along "y-axis" and "x" along "x-axis")

    U is a complex function of "x"
    as U= a(x)+i b(x)
     
  5. Jul 28, 2011 #4
    so, what is the value of x at the time you evaluate U?
     
  6. Jul 28, 2011 #5
    "x" is the having range from 0-5
     
  7. Jul 28, 2011 #6
    no...you do that AFTER you evaluated U
     
  8. Jul 28, 2011 #7
    what about my statement that U is not really a matlab function? You as a human know that U depends on x, but you have simply evaluated an equation with x in it, calculated a value and assigned that value to a variable U

    ...at least that the way I see it.

    if you want U to be a proper matlab funtion of x, I think you need to delcare it as so (need keyboard 'function', I think) and show arguments, etc....and THEN, you can pass x at the time of plotting, something like plot(x, Re(U(x)) ), I presume.
     
  9. Jul 28, 2011 #8
    "U" is a function of x and I want to draw graph of U against "x",
    If i evaluate U for some fixed value of "x" then you can fix any value for "x" that could be 3
     
  10. Jul 28, 2011 #9
    But -- here's the problem (or one of the problems) -- it isn't. Not in MATLAB, that is. You haven't told MATLAB that U is a function of x, not in any way that MATLAB understands.

    Have you ever plotted anything in MATLAB? Can you, for instance, plot y = x^2?

    gsal is right: the syntax that you posted makes no sense as a way of generating a plot. Work out how to do that first.
     
  11. Jul 29, 2011 #10
    Ohh, ok
    I am using MATLAB first time, normally I used mathematica ,
    Ok I will try y=x^2 first and try to understand the language of MATLAB,

    In the equation which I wrote up there, U is represented in terms of J and J is depending on x
    Thanks brothers for your kind support, if still you think of any way to teach me how to draw this function, Please let me now

    Regards
     
  12. Jul 29, 2011 #11
    friends, I did it.
    y1=1.9417+3.5012*i;
    y2=1.9417+3.5012*i;
    y3=4.7348-1.4837*i;
    y4=4.7345+1.4837*i;
    y5=202.701;
    m1=1.558*10^12-1.90339*10^12*i;
    m2=1.536*10^12+1.8116*10^12*i;
    m3=-6.0446*10^11+4.0463*10^12*i;
    m4=-4.134*10^11-3.954*10^12*i;
    m5=-2.674*10^8-1.222*10^8*i;
    a=1;
    O1=0.023475-0.0252192*i;
    O2=0.023475+0.0252192*i;
    O3=-0.0225775-0.0197677*i;
    O4=-0.0225775+0.0197677*i;
    O5=-0.000015578;
    w=2;
    t=0.1;
    z=1;

    x=1:1:5;
    j=(i*a*O1-y1)*m1*exp(-y1*x)+(i*a*O2-y2)*m2*exp(-y2*x)+(i*a*O3-y3)*m3*exp(-y3*x)+(i*a*O4-y4)*m4*exp(-y4*x)+(i*a*O5-y5)*m5*exp(-y5*x);
    u=j*exp(w*t+i*a*z);
    % x=linspace(0,5);
    plot(x,u,'bo-')

    Thanks for your help
     
  13. Jul 29, 2011 #12
    once again, dear fellows if i have any other function say W and want to plot u and W both on one graph what would be the command for that,
    I have used plot ( x, u, 'b*-',W, 'ro-' ) but it did not work,
    where W = j*5*O1
     
  14. Jul 29, 2011 #13
    There's this common perception that MATLAB and Mathematica are alternative systems that do pretty much the same thing. This is wrong. They work very differently, they're programmed very differently, and they're not alternatives. Mathematica is really specialized for doing math. It works with symbols. MATLAB is for doing computation, and is more like a conventional programming language. It can't work with symbols. It may seem like it does, but actually, in MATLAB, as in most programming languages, a name like U is just a way of designating where in the computer something is stored.
     
  15. Jul 29, 2011 #14
    not to be mean, but there is also something in matlab called on-line help that for basic stuff like this I bet it works wonders...just search for function.
     
  16. Jul 29, 2011 #15
    I got it and thanks brothers it really help.
     
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