How to generate plot

I am trying to generate a plot with K1 in the y axis and x in the x axis. My code will pull up a figure but it doesn't plot along the points. Any tips?

Answer 1

[Voss]

Original code (with disps removed):

K1 = 0;
a = 5;
n = 30;
P0 = 100;
c = 3;
for i = 1:30
    s = cos(((2*i-1)*pi)/(2*n));
    x = s*a;
    P = P0*(exp((-0.5)*(x/c)^2))*(1-(x/c)^2);
    K1 = K1+(sqrt(pi*a)*(1/n)*P*(1+s));
    figure(1)
    plot(x,K1)
    grid
    title('K1 as a function of crack length')
end

You're plotting 30 lines, but each line contains only one point and the lines don't have any data marker. A single point with no marker doesn't show up. Also, each line replaces the previous line plotted.

To fix these things, you could include a data marker in your plot calls and call hold on to keep all the lines:

K1 = 0;
a = 5;
n = 30;
P0 = 100;
c = 3;
for i = 1:30
    s = cos(((2*i-1)*pi)/(2*n));
    x = s*a;
    P = P0*(exp((-0.5)*(x/c)^2))*(1-(x/c)^2);
    K1 = K1+(sqrt(pi*a)*(1/n)*P*(1+s));
    figure(1)
    plot(x,K1,'.') % '.' data marker
    hold on        % use hold on to preserve existing lines
    grid
    title('K1 as a function of crack length')
end

However, it's better (and I imagine more like what's intended) to do a vectorized calculation for x and K1 and plot them all at once:

% K1 = 0; % no longer needed
a = 5;
n = 30;
P0 = 100;
c = 3;

i = 1:30;
s = cos(((2*i-1)*pi)/(2*n));
x = s*a;
P = P0*(exp((-0.5)*(x/c).^2)).*(1-(x/c).^2); % use element-wise operations (.*, .^) to calculate all values at once
K1 = cumsum(sqrt(pi*a)*(1/n)*P.*(1+s));      % use cumsum (cumulative sum) to add the sequence of K1 values

figure()    % (making a new figure this time)
plot(x,K1)  % no data marker (but you could still use one if you want)
grid
title('K1 as a function of crack length')

Answer 2

[Torsten]

a = 5;
n = 30;
P0 = 100;
c = 3;
s = cos((2*(1:n)-1)*pi/(2*n));
x = a*s;
P = P0*exp(-0.5*(x/c).^2).*(1-x/c).^2;
K1 = sqrt(pi*a)/n*cumsum(P.*(1+s));
plot(x,K1)
grid
title('K1 as function of crack length')

[Voss]

Note that you have:

(1-x/c).^2

But OP's code has:

(1-(x/c)^2)

(Things like this is why it's better for OPs to share code as text rather than an image.)

[Torsten]

(Things like this is why it's better for OPs to share code as text rather than an image.)

The main reason is to get an answer at all ...