Unable to perform assignment because the left and right sides have a different number of elements. Error in Hyperverlocitynew (line 36)

Question

James Murray 2020-7-31

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回答： Rohit Pappu 2020-8-14

n=1000; %number of iterations 
x=zeros(n); % horizontal distance traveled
y=zeros(n); % vertical distance traveled
vx=zeros(n); % horizontal velocity
vy=zeros(n); % vertical velocity
v=zeros(n); % total velocity
theta_th=0.6575; % launch angle
vx(1)=7815.06*cos(theta_th); % starting x velocity
vy(1)=7815.06*sin(theta_th); % starting y velocity
x(1)=0; % starting x position 
y(1)=0; % starting y position
delta_t=0.0001; % step size
a=(pi/4)*(3/12)^2; % area of projectile
m=55/32.174; % mass of projectile
g=32.174; % gravity
k=1.4; % 
R=1716.5; % ideal gas constant
for i=2:n
   
    [T,p,rho]=atmos_funEE; %
    c=sqrt(k*R*T); % speed of sound
    ma=v(n)/c; %
    if (0<ma)&&(ma<=0.8) %
    cd=0.17; %
    elseif (0.8<ma)&&(ma<=1.2) %
    cd=0.7763*ma-0.451; %
    elseif (1.2<ma)&&(ma<=8) %
    cd=0.0093*ma^2-0.1223*ma+0.607; %
    end
    x(i)=(x(i-1))+(delta_t*(vx(i-1))); %
    vx(i)=(vx(i-1))+(delta_t*(-1/2)*rho*a*cd*(v(i-1))*(vx(i-1))*(1/m)); %
    y(i)=(y(i-1))+(delta_t*(vy(i-1))); %
    vy(i)=(vy(i-1))+(delta_t*(-g-(1/2)*rho*a*cd*v(i-1)*(vy(i-1))*(1/m))); %
    v(i)=sqrt((vx(i-1))^2+(vy(i-1))^2); %
end 

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Alan Stevens 2020-8-2

I've just noticed that you have defined x, y, etc. as zeros(n). This will result in matrices of size nxn for each of them. Is this what you meant, or did you mean zeros(1,n), which will result in vectors of size 1xn?

Walter Roberson 2020-8-2

You are not passing anything into the function. How can it be calculating correct coefficients?

The current hypothesis is that rho is a non-scalar

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Answer 1

Rohit Pappu 2020-8-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/573577-unable-to-perform-assignment-because-the-left-and-right-sides-have-a-different-number-of-elements#answer_479880

As per my understanding, you are unable to assign the value of the equation to vx(i). The error might have occurred because the variable cd is declared conditionally and thus it behaves like a matrix.

A plausible solution would be to declare cd outside the loop which would make the variable remain as a scalar.