Graph Not Plotting for the For Loop Code
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I'm trying to plot a graph of air density against altitude using the following density altitude eq on the NASA website:
This is the code I've written:
global rho
for h = 0:10:40000
if (h < 11000)
T = 25.05 - h.*0.00649;
p = 101.29* ((T + 273.15)./288.08)^5.256;
else
if (11000 < h) & (h< 250000)
T = -56.46;
p = 22.65* exp(1.73 - h.*0.000157);
else
if (h > 25000)
T = -131.21 + h.*0.00299;
p = 2.488*((T + 273.15)/216.6)^-11.3888;
end
end
end
rho = p / (0.2869*(T + 273.15));
end
plot (h,rho)
xlabel('height')
ylabel('Density')
But nothing is showing up on the graph plot. What am I missing?
采纳的回答
"What am I missing? "
Assigning the values to an output array via indexing.
Because you did not use indexing to assign the values to an array your code simply overwrites the previous iteration's values until the final iteration, leaving you with one data value (which is not visible when plotted as the default line has no marker).
This works and plots all of the loop results (only you can check if it is correct):
G = 6.67408e-11; % Universal Gravitational Constant
M = 5.9722e24; % Mass of the earth
R = 6371e3; % Radius of the earth(m)
A = 21*pi; % Area of the rocket
Cd = 0.4; % Drag Coefficient for the rocket
t = 0:1:4000;
h_v = 0:100:5000;
rho = nan(size(h_v)); % <--- preallocate the output array
for k = 1:numel(h_v) % <--- loop over indices, not data values
h = h_v(k);
if (h < 11000)
T = 25.05 - h.*0.00649;
p = 101.29* ((T + 273.15)./288.08)^5.256;
else
if (11000 < h) & (h< 250000)
T = -56.46;
p = 22.65* exp(1.73 - h.*0.000157);
else
if (h > 25000)
T = -131.21 + h.*0.00299;
p = 2.488*((T + 273.15)/216.6)^-11.3888;
end
end
end
rho(k) = p / (0.2869*(T + 273.15));
% ^ use indexing to assign output to an array
end
plot (h_v,rho)
xlabel('height')
ylabel('Density')
Logical indexing may be a simpler approach than using a loop.
2 个评论
Asit Rahman
2022-2-21
Torsten
2022-2-21
I think you will have to replace
if (11000 < h) & (h< 250000)
by
if (11000 < h) & (h< 25000)
更多回答（2 个）
H=linspace(0,40000,4001)
rho=zeros(1,numel(H))
for i=1:numel(H)
h = H(i);
if h > 25000
T = -131.21 + h.*0.00299;
p = 2.488*((T + 273.15)/216.6)^-11.3888;
elseif h<= 25000 && h>11000
T = -56.46;
p = 22.65* exp(1.73 - h.*0.000157);
else
T = 25.05 - h.*0.00649;
p = 101.29* ((T + 273.15)./288.08)^5.256;
end
rho(i) = p / (0.2869*(T + 273.15));
end
plot(H,rho)
Arif Hoq
2022-2-21
your output is a single value. if your code is going well then try this with a marker
plot (h,rho, 'o')
2 个评论
G = 6.67408e-11; % Universal Gravitational Constant
M = 5.9722e24; % Mass of the earth
R = 6371e3; % Radius of the earth(m)
A = 21*pi; % Area of the rocket
Cd = 0.4; % Drag Coefficient for the rocket
t = 0:1:4000;
%h = 9.8*t.^2;
%h = 0:100:5000;
for h = 0:10:4000
if (h < 11000)
T = 25.05 - h.*0.00649;
p = 101.29* ((T + 273.15)./288.08)^5.256;
else
if (11000 < h) & (h< 250000)
T = -56.46;
p = 22.65* exp(1.73 - h.*0.000157);
else
if (h > 25000)
T = -131.21 + h.*0.00299;
p = 2.488*((T + 273.15)/216.6)^-11.3888;
end
end
end
rho = p / (0.2869*(T + 273.15));
end
plot (h,rho, 'o')
xlabel('height')
ylabel('Density')
Asit Rahman
2022-2-21
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