Trouble plotting multiple graphs

Question

Josie 2014-8-20

0
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https://ww2.mathworks.cn/matlabcentral/answers/151622-trouble-plotting-multiple-graphs

编辑： Patrik Ek 2014-8-20

I trying to plot multiple graphs of mass vs drag. I know the equation is correct but the plot's shouldn't be coming out with negative drag. Is there something wrong with the code?

M=linspace(0,1,100);
g=10;
for A=0.1:0.1:0.9
    s=(A-0.5)*M.*g-(A^2)/4;
    theta=s./(2*M.*(A-0.5)^2+2*M+(A^2-A+1/3)/2);
    D=(-A.^2+A-1/3).*theta-0.5*A.^2;
    plot(M,D)
    axis([0,1,-2,2])
    hold all
end
legend('A=0.1','A=0.2','A=0.3','A=0.4','A=0.5','A=0.6','A=0.7','A=0.8','A=0.9')

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Patrik Ek 2014-8-20

编辑：Patrik Ek 2014-8-20

在 MATLAB Online 中打开

The equation for D is quite simple assuming theta is an independent variable, which it of course not is, since it is calculated. Still it can be treated as such to calculate D(theta), since D does not rely on M except for the dependence in theta. You can look at equation D as a function of theta and find out how D varies with theta.

This can be done by creating a vector theta = -2*pi:0.01:2*pi and use it as input to D. By plotting

plot(theta,D);

you will then see how D depends on theta for different values of A. With the help of these graphs you can see if the result is reasonable.

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