# no data plots on graph (plot (x,y))

조회 수: 3 (최근 30일)
Jocelyn . 2020년 11월 8일
댓글: Rafael Hernandez-Walls . 2020년 11월 8일
Hello,
When I run my code, the 'Figure' graph box pop up however there is no data/lines on the graph. I am trying to plot the acceleration, velocity, and altitude of a paratrooper falling out of a plane as a function of time.
Below is my code:
d = 32000;
H = 8000;
Re = 6370000;
%c2 = 0.5*exp(-d/H);
g = 9.8*((1+(d/Re))^2);
Dt = 0;
t = 0;
%Vt = sqrt(g*m/(0.5*exp(-d/H));
dt = 0.0001;
while d > Dt
v = (sqrt((9.8*((1+(d/Re))^2))*m/(0.5*exp(-d/H))))*tanh((9.8*((1+(d/Re))^2))*t/(sqrt((9.8*((1+(d/Re))^2))*m/(0.5*exp(-d/H)))));
d = d + (v*dt);
if d == Dt
break
else
t = t+dt;
d = d + (v*dt);
end
end
disp('time until ground impact (seconds): ')
disp(t)
plot(d,t)
plot(v,t)
plot((v/t),t)
Full question that I was trying to get the above code to solve was: calculate the time of fall until the ground impact, given c2 scales with atmospheric density as c2 =0.5exp(-d/H), where H= 8km is the scale height of the atmosphere and d is the height above the ground. Furthermore, assume that g is no longer constant but is given by g = 9.8/(1+(d/Re))^2 where Re = 6370km is the radius of the earth. Plot the acceleration, velocity, and altitude of the paratrooper as a function of time.
##### 댓글 수: 2이전 댓글 1개 표시이전 댓글 1개 숨기기
Jocelyn 2020년 11월 8일
Thank you. This value was previously saved (it's 70) in the command window, so my code was running even though I did not program it on this script.

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### 채택된 답변

Rafael Hernandez-Walls 2020년 11월 8일
David is correct. Why don't you try something like that in your code...
d(1) = 32000;
H = 8000;
Re = 6370000;
%c2 = 0.5*exp(-d/H);
Dt = 0;
t(1) = 0;
%Vt = sqrt(g*m/(0.5*exp(-d/H));
dt = 0.0001;
m=70;
indice=1;
while d(indice) > Dt
g = 9.8*((1+(d(indice)/Re)).^2);
v(indice) = (sqrt((9.8*((1+(d(indice)/Re))^2))*m/(0.5*exp(-d(indice)/H))))*tanh((9.8*((1+(d(indice)/Re))^2))*t(indice)/(sqrt((9.8*((1+(d(indice)/Re))^2))*m/(0.5*exp(-d(indice)/H)))));
d(indice+1) = d(indice) + (v(indice)*dt);
if d(indice+1) == Dt
break
else
t(indice+1) = t(indice)+dt;
d(indice+1) = d(indice) + (v(indice)*dt);
end
indice=indice+1;
end
disp('time until ground impact (seconds): ')
disp(t(indice))
v(indice)=[];
plot(d,t)
figure
plot(v,t)
figure
plot((v./t),t)
##### 댓글 수: 1없음 표시없음 숨기기
Rafael Hernandez-Walls 2020년 11월 8일
v(indice)=[];
put this
t(indice)=[];
d(indice)=[];

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### 추가 답변 (1개)

David Hill 2020년 11월 8일
You need to run your code using arrays for t, g, v, and d.
##### 댓글 수: 1없음 표시없음 숨기기
Jocelyn 2020년 11월 8일
How do I save the data being continually updated in the while loop into an array so I can use this array in the plot function?

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