In the following sample. The result of the graphic is one point What is wrong here please

                  energy = energy + deltaE;   

     for A = 1:nPart

  th=A*L;

     end

plot(energy,A,'b*')
xlabel('energy')
ylabel('( th)')

              end

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

[Stephen23]

zina shadidi's "Answer" moved here:

thank you Image Analyst and Walter Roberson

nPart = 100;        % Number of particles
density = 0.85;     % Density of particles

maxDr = 0.1;
printFreq = 100;
nSteps = 500;

function [coords, L] = initCubicGrid(nPart,density)
coords = zeros(3,nPart);
L = (nPart/density)^(1.0/3);
nCube = 2;
while (nCube^3 < nPart)
  nCube = nCube + 1;
end

index = [0,0,0]';

for part=1:nPart
  coords(:,part) = (index+[0.5,0.5,0.5]')*(L/nCube);
  
  index(1) = index(1) + 1;
  if (index(1) == nCube)
    index(1) = 0;
    index(2) = index(2) + 1;
    if (index(2) == nCube)
      index(2) = 0;
      index(3) = index(3) + 1;
    end
  end
end

end

energy = LJ_Energy(coords,L);

for step = 1:nSteps
  if (mod(step,printFreq)==0)
    step;
  end
  for i=1:nPart
    rTrial = coords(:,i) + maxDr*(rand(3,1)-0.5);
    rTrial = PBC3D(rTrial,L);
    deltaE = LJ_EnergyChange(coords,rTrial,i,L);
    if (rand < exp(-beta*deltaE))
      coords(:,i) = rTrial;
      energy = energy + deltaE;
      % A= number of layers, th=thin film thickness
      for A = 1:nPart        
        th=A*L;        
        figure;
        plot(th,energy, 'b*'); % Plot the calculated solution
        ylabel('energy');
        xlabel('th');
      end
    end
  end
end

[Image Analyst]

Where do you call initCubicGrid() and what do you pass in for nPart and density?

Answer 1

[Walter Roberson]

Each iteration of the loop, you are overwriting all of th.

But that does not matter because you do not use the value of th later.

When you use a for loop, after the loop is done, the loop variable is left at the last value it had within the loop, which would be a scalar in this case (and in most cases.) We cannot tell whether energy is a scalar or a vector, but A will be a scalar at the time of the plot()

[zina shadidi]

Its th in this line plot(energy,th,'b*') sorry it was a Typing error (just here) However, I have the same problem

[Image Analyst]

Put these lines before that and tell us what it says

whos energy
whos th

Answer 2

[Image Analyst]

Maybe you meant

for A = 1:nPart
    th(A) = A * L;
end
plot(energy, th,'b*-');
grid on;

assuming both energy and th are both vectors. If energy is a single number, you'd get an error trying to plot th against it.

But we can't tell because you left out most of the code. Attach complete code if you want a complete answer.