loop for specific values

Hello everyone!

Please, could you help me with a code.

I need to calculate for a given set of values V and P. So, my set is phi = [0;36.87;48.19;55.15;60]

My code is:

clear all; close all
W = 10000;
S = 40;
AR=7;
cd0 = 0.005;
k = 1 / pi / AR;
Psl=25000;
clalpha = 2*pi;
rho=1.225;
figure(1);hold on; xlabel('V');ylabel('P')
for phi = [0;36.87;48.19;55.15;60]
    i=0;
    for alpha = 1:0.25:12
        i=i+1;
        n(i)=1/cos(phi*pi/180);
        cl(i) = clalpha * alpha * pi/180;
        V(i) = sqrt(2*n(i)*W/rho/S/cl(i));
        L(i) = 0.5 * rho * V(i) * V(i) * S * cl(i);
        cd(i) = cd0 + k * cl(i) * cl(i);
        D(i) = 0.5 * n(i)*rho * V(i) * V(i) * S * cd(i);
        clcd(i) = cl(i)/cd(i);
        p(i) = D(i)*V(i);
        P_a(i)=Psl;
    end
    figure(1); plot(V,p)
    hold on 
    plot(V,P_a)
end

Answer 1

[Dyuman Joshi]

From the for loop documentation - "To iterate over the values of a single column vector, first transpose it to create a row vector."

Thus, transpose the input such that it is provided as a row vector for the iterating values and your code will work.

Also, you can vectorize the inner for loop like I have shown -

W = 10000;
S = 40;
AR = 7;
cd0 = 0.005;
k = 1 / pi / AR;
Psl = 25000;
clalpha = 2*pi;
rho = 1.225;
figure(1);
hold on;
xlabel('V');ylabel('P');

%Bring out the constant values out of the loop
alpha = 1:0.25:12;
cl = clalpha*alpha*pi/180;
cd = cd0 + k * cl.^2;
clcd = cl./cd;
P_a = Psl*ones(size(alpha));


for phi = [0;36.87;48.19;55.15;60]'
%                        transpose^
    n=1/cos(phi*pi/180);
    V = sqrt(2.*n.*W./rho./S./cl);
    L = 0.5*rho*V.^2*S.*cl;
    D = 0.5.*n.*rho.*V.^2*S.*cd;
    p = D.*V;
    plot(V,p);
    plot(V,P_a);
end

Answer 2

[Robert]

@ geometry dash scratch

Hello, Here's the modified code with some improvements:

clear all; close all

W = 10000;

S = 40;

AR = 7;

cd0 = 0.005;

k = 1 / (pi * AR);

Psl = 25000;

clalpha = 2 * pi;

rho = 1.225;


figure(1);

hold on;

xlabel('V');

ylabel('P');


phi = [0; 36.87; 48.19; 55.15; 60];


for k = 1:numel(phi)
    
    alpha_range = 1:0.25:12;
    
    n = 1 / cos(phi(k) * pi / 180);
    
    
    cl = clalpha * alpha_range * pi / 180;
    
    V = sqrt(2 * n * W / (rho * S * cl));
    
    L = 0.5 * rho * V.^2 * S .* cl;
    
    cd = cd0 + k * cl.^2;
    
    D = 0.5 * n * rho * V.^2 * S .* cd;
    
    clcd = cl ./ cd;
    p = D .* V;
    P_a = Psl * ones(size(V));
    
    
    figure(1);
    
    plot(V, p);
    
    hold on;
    
    plot(V, P_a);
    
end