Need MATLAB help for assignment

𝐹𝑝(𝑛) 𝐹𝑑 = 16/3 ( 1/𝐶𝐷 ) 1/(𝑏⁄𝐷5) ( 𝑉0/𝑢 )^ 2 ( 1/𝑅 )^ 3 √( 1/𝑅 )^4 − 2 ( 1/𝑅)^ 2 cos 2𝜃 + 1

Fp(n)/Fd = the ratio between radial pressure and bed forces

CD = drag coefficient (assume it is 1.0 for this problem)

V0/u = the ratio between upstream velocity and velocity near the pile (assume this term = 1.0);

R = the radius from the pile (in cylindrical coordinates)

𝜃 = the angle from the pile (in cylindrical coordinates)

Plot contours of the above expression for b/D50 ratios of [0.1, 1.0, 10, 100] for radii up to 5.0 m using a function to perform all computations for this expression. I am aware that we have not formally done contours yet, but we have done surface plotting (in class one day; check your notes). Type help contour to see how the command works. I am testing your ability to learn and apply a new command here.

Present your results using a 2x2 subplotted plotting window. Label your contours using the command ‘clabel’ (type ‘help clabel’ to learn the proper syntax). Be sure to give your plots proper titles and x,y labels.

this is the code i have so far

function F = MidtermGraph(R,theta,bD)
bD = [0.1, 1.0, 10, 100];
R = (1:1.25:5);
c = R;
a = 1/2*bD;
b = abs(sqrt(c.^2 - a.^2));
theta = abs(atan(b./a));
for r = 1:length(R)
  for b = 1:length(bD)
    F = (16/3).*(1./bD).*(1./R).^3.*abs(sqrt((1./R).^4-2.*(1./R).^2.*cos(2.*theta)+1));
  end
end

[F] = MidtermGraph(R,theta,bD);
              for b = 1:length(bD)
               figure(1)
               subplot(2,2,b)
               x = R.*cos(theta);
               y = R.*sin(theta);
               z = F;
               [x,y,z] = meshgrid(x,y,z);
               [C,h] = contour(R,theta,bD,x,y,z);
               clabel(C,h);
               grid on
               xlabel('b/D50')
               ylabel('radii')
               title('Radial Pressure vs. Bed Forces')
              end

[Walter Roberson]

Editing away your question is not the way to thank a volunteer for taking the time to analyze your code and describe what is wrong with it and what is needed to do in order to repair it. :(

[Rik]

I restored your edit from the Google cache. Don't edit away your question again, that is extremely rude.

http://web.archive.org/web/20210310082105/https://www.mathworks.com/matlabcentral/answers/766826-need-matlab-help-for-assignment

Answer 1

[Walter Roberson]

for r = 1:length(R)
  for b = 1:length(bD)
    F = (16/3).*(1./bD).*(1./R).^3.*abs(sqrt((1./R).^4-2.*(1./R).^2.*cos(2.*theta)+1));
  end
end

That code is overwriting all of F in every iteration.

Both of your functions have the same name.

Your second function asks to return F but does not calculate F. It also needs the value of F but F is not input or output.

[Walter Roberson]

Most of the time it is best to structure the code into at least two parts. One of the parts is the user interface, asking the user for any relevant inputs, calling the second part to do the calculations, and then either doing the plotting or calling a third part to do the plotting. The second part would be the pure calculation. If you construct a third part, make it pure plotting.