Unable to plot graphs

%S-N Graph Plot for Fatigue Testing for the three specimens 

%Defined Parameters
disp('The dimensions and parameters of the Test:');
disp('The diameter for each of the specimen, D=5mm');
disp('The distance from the end of the specimen and the minimum diameter of the specimen, L = 78mm');

D = 5; L = 78; N=5;

%The weight that are loaded (kg) are then later converted to Newton (N)
disp('The weight in Newton (N) applied on each of the specimen');
P = [7.580811,9.02244,10.38561,13.20022,14.63204];

disp('Using the Defined Parameters for all the value of (P), the stress is calculated using the formula of stress');

S = [240.8874,286.6965,330.0126,419.4494,464.9469];

%Determining the Number of Cycles done by the three Specimens

disp('The number of cycles done with stress applied and number of trials for Mild Steel');
for f = 1:N
    Ms(f)=input(['Load Number:'num2str(f)','Cycles done:']);
    f=f+1;
end 

disp('The number of cycles done with stress applied of trials for Aluminium');
for d = 1:N
    Ali(d)=input(['Load Number:'num2str(d)',Cycles Done:']);
    d = d+1;
end 
        
disp('The number of cycles done with stress applied and number of trials for Brass');
for g = 1:N-1
   Brs(g)=input(['Load Number:'num2str(g)',Cycles Done: ']);
   g = g+1;
end
  
%Arranging allt he values 
disp('The Number Of Cycles taken by Aluminium');
disp(Ali);
disp('The Number Of Cycles taken by Mild Steel');
disp(Ms);
disp('The Number of Cycles taken by Brass');
disp(Brs);

%Plotting the S-N Curve for the three Specimens 
%For Aluminium 
figure 
plot (Ali,S)
title('S-N graph (ALuminium)')
xlabel('Number of Cycles (N)')
ylabel('Stress Applied (N/mm^2)')

Answer 1

[Jan]

for f = 1:N
    Ms(f)=input(['Load Number:'num2str(f)','Cycles done:']);
    f=f+1;
end 

This is not the way for loops work in Matlab. Omit the line f=f+1, because it does not do anything useful here. The loop counter is increased by the for command already:

for k = 1:5
   disp(k)
end

I've formatted the code in your question (please do this by your own in following questions). Immediately you can see a problem with the syntax:

    Ali(d)=input(['Load Number:'num2str(d)',Cycles Done:']);        

The syntax highlighting shows you, that the right string is not properly enclosed in quotes. The quote directly behind a variable or closing parenthesis or square bracket is interpreted as transposition (to be exact: as conjugate transposition). Prefer to separate parts of concatenations by commas to increase the clarity:

     Ali(d)=input(['Load Number:', num2str(d), 'Cycles Done:']);     

I'd prefer:

     Ali(d) = input(sprintf('Load Number: %d Cycles Done:', d));     

If the code has such a syntax error, it does not run at all, but trying to start it produces an error message. Then the description "unable to plot graphs" does not hit the point.

[Abdullah Hassan]

thank u very much