my code is running but it doesnt show the exponential graph .it shows nothing at the graph.

    filename = 'datacollect2.xlsx';
    num = xlsread(filename,'B1:B60');
    w = num/60;
    N = length(num);
    t = 1/w;
    s = xlsread(filename,'B3:B3');
    xt= s;
    g = 1/N;
    i = xt + num;
    h = xt/ i ;
    ln=@log;
    q=ln(h);
    zeta = g * q;
    j= 1-power(zeta,2);
    wd = w*power(j,1/2);
    r = bsxfun(@rdivide,w,wd);
    k = zeta*r;
    l=sin(wd);
    u=k*l;
    m=bsxfun(@plus,cos(wd),u);
    n= - zeta*w;
    plot (1 - exp(n)*(m))

Answer 1

[Walter Roberson]

You are using the / operator in several places. In MATLAB, A/B is more or less the same as A * pinv(B) . 1/w where w is 60 x 1, gives you a 1 x 60 result. Likewise, h = xt/ i where i is 60 x 1, gives you a 1 x 60 result. You then end up working with this mix of 60 x 1 and 1 x 60 and you end up with trying to combine arrays in the wrong way.

>> 1/[2;4;3]
ans =
                         0                      0.25                         0

Notice the output is a row vector for a column vector divisor.

If you would need the answer [0.5; 0.25; 0.3333] (column vector, individual divisions) instead for this calculation, then you need to use the ./ operator

Because of this, in your

h = xt/ i ;

most of the entries will be 0. When you have A/B with scalar A and column vector B, the result turns out to always be a row vector where each entry is 0 except for the single entry located where B first reaches its largest absolute magnitude, [~, idx] = max(abs(B)), and that one location of the result is 1./B(idx) .

With all of those 0 floating around in h, ln(h) is mostly -inf . Then when you start doing more matrix multiplications on the matrices with -inf you end up with situations where you have (-inf) - (-inf) which is NaN. So your output matrix m comes out all NaN. Then there are no non-NaN entries for the plotting to work on.

It is almost certain that you should be mostly using ./ operators instead of / operators . If you are absolutely sure that you want / operators then you should comment those lines and you should comment the purpose of your code and the methods, as otherwise people like me are going to come along and assume that your code is broken.

[arif hussain]

it works thank you Walter Roberson. i am using this ./ that plot but when i importing the another excel file it shows empty graph again.

Answer 2

[Matt J]

Inspect the plotted expression from the command line.

 >> disp( 1 - exp(n)*(m) )

Maybe it doesn't contain anything that can be plotted.