loop for specific values
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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
回答（2 个）
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
Robert
2023-11-28
编辑：Walter Roberson
2025-7-3
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
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2025-7-3
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