Empty plot returning when I try to graph

funciton code

function G = sigmayytheta0(rr) %why did we even need sigma_0 in the first place..?
    K = 0.5605;
    G = (K/sqrt(2*pi*rr)); %when theta = 0, everything including theta simplifies to 1
end

script code

%sigmayy along theta = 0 degrees 
for i = 1:1000;
 for j = 1:1000;
  x = i/1000;
  y = (j-500)/1000;
  xtip = x - .1;
  rr = sqrt(xtip^2+(y^2)); 
  M = sigmayytheta0(rr);
  hold on
    end
end


figure(2)
plot(rr,M, "--");
hold off
xlabel('r')
ylabel('sigmayy')
title('Sigmayy versus r at theta = 0');

Answer 1

[Kevin Holly]

%sigmayy along theta = 0 degrees 
for ii = 1:10;
    for jj = 1:10;
    x = ii/1000;
    y = (jj-500)/1000;
    xtip = x - .1;
    rr(ii,jj,:) = sqrt(xtip^2+(y^2)); 
    M(ii,jj) = sigmayytheta0(rr(ii,jj));
    figure(1)
    scatter(rr(ii,jj),M(ii,jj),'.b');
    hold on
    end
end
hold off
xlabel('r')
ylabel('sigmayy')
title('Sigmayy versus r at theta = 0');

figure(2)
plot(rr,M, "--");
% hold off   - remove this hold off
xlabel('r')
ylabel('sigmayy')
title('Sigmayy versus r at theta = 0');

function G = sigmayytheta0(rr) %why did we even need sigma_0 in the first place..?
    K = 0.5605;
    G = (K/sqrt(2*pi*rr)); %when theta = 0, everything including theta simplifies to 1
end

Answer 2

[Walter Roberson]

  M = sigmayytheta0(rr);

Every iteration in i and j, you are overwriting all of M. At the end, your M will be a scalar.

You should be storing into something indexed with i and j. Likewise with rr

  plot(rr,M, "--");

If you assign to rr and M indexed by i and j, you are going to end up with a 2D array, but plot() is for drawing lines. Do you want to draw a scatter plot? Perhaps you want to draw a contour plot? Or a surface plot?

Note that there will be a number of different locations that come out to the same rr value. You are calculating a radius from i = 10, j = 500 and that is going to be radially symmetric.

Answer 3

[David Hill]

[i,j]=meshgrid(1:1000);
xtip=i/1000-.1;
y=(j-500)/1000;
rr=hypot(xtip,y);
K=.5605;
M=K./(sqrt(2*pi*rr));
plot(rr,M, "--");
xlabel('r')
ylabel('sigmayy')
title('Sigmayy versus r at theta = 0');