Can someone please check my code, not quite sure where im going wrong

clc
clear
%--------------------------------------------------------------------------------------------------------%
p = 1.2;   %variables given to me in question
g = 9.81;
m = 77;
c = 1;
a1 = .7; 
a2 = 50; 
t1 = 50;
t2 = 70;
v0 = 50;
h0 = 2.5;
T = .005;
tmid = (t1+t2)/2; %formula gives to find what t mid is
%--------------------------------------------------------------------------------------------------------%
A = @(t) 1/2*(a2-a1)*tanh(10.*((t-tmid)/((t2-t1))))+(1/2*(a2+a1));
T1 = 0:1:120; %used for plotting x axis
D = @(T1)(p*c.*(A(T1)))/2*m; %drag constant
plot(T1, A(T1), 'b-', 50, .7, 'ro', 70, 50, 'ro') %t1 occurs at 50 seconds in, the area is .7 so I used that as a y co-ordinate and 50 as my x, marking that spot with a red circle.
axis([0 120, .6 70]); 
xlabel('Time')
ylabel('Area')
title('Area over Time')
%--------------------------------------------------------------------------------------------------------%
x(1) = 0;, vx(1) = v0;, y(1) = 0;, vy(1) = 0; %initial variables used to start the loop
for n=1 %initialize time index
    while 1 %forever while loop
        if y(n) > h0, break; end % break when ground is reached
        tn = (n-1)*T; %nth time instant in seconds
        t(n) = tn;  %build time vector, needed for plotting
        Dn = D(n).*(tn); %drag constant in time tn
        v = sqrt(vx(n)^2+vy(n)^2); %problem tells me to write "no need to save V in an array"- not sure what this means
        ax(n) = -Dn * vx(n)*v; %horizontal acceleration
        v(n) = sqrt(vx(n)^2+vy(n)^2); 
        ay(n)= -(D(tn)) * vy(n)*v(n)+g; ; 
        x(n+1) = x(n)+T*vx(n);
        vx(n+1)= vx(n)+T*ax(n);
        y(n+1)=y(n)+T*vy(n);
        vy(n+1)= vy(n)+T*ay(n);
        n = n+1; %updates the index to use N+1, so second round will use 2 for N, as N is defined as 1, N= 1+1, whill use 2 for N in next loop and so on. 
    end 
end
%--------------------------------------------------------------------------------------------------------%
Vc_1 = sqrt((2*m*g)/p*c*A(30));
Vc_2 = sqrt((2*m*g)/p*c*A(80));
Vc_3 = sqrt((2*m*g)/p*c*a1);
Vc_4 = sqrt((2*m*g)/p*c*a2);

[Steven Lord]

What does "going wrong" mean?

• Do you receive warning and/or error messages? If so the full and exact text of those messages (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warning and/or error.
• Does it do something different than what you expected? If so, what did it do and what did you expect it to do?
• Did MATLAB crash? If so please send the crash log file (with a description of what you were running or doing in MATLAB when the crash occured) to Technical Support using the telephone icon in the upper-right corner of this page so we can investigate.

[Daniel Martelli]

So yes it did crash, but i already reported it. Okay, so, since i saved it, there is no problem now

[Daniel Martelli]

The other problem is, i dont quite know if im getting correct loop values

[Walter Roberson]

To be honest, very very few people are going to read through four pages of images of textbook questions, and figure out how those pages connect to your code, and work through to decide whether your code is correct for the situation or not.

The volunteers here work best on very focused problems.

[Daniel Martelli]

do you know which textbook this is?

[Image Analyst]

Your code does not crash. And MATLAB itself did not crash. Your code produced this plot:

clc
clear
%--------------------------------------------------------------------------------------------------------%
p = 1.2;   %variables given to me in question
g = 9.81;
m = 77;
c = 1;
a1 = .7; 
a2 = 50; 
t1 = 50;
t2 = 70;
v0 = 50;
h0 = 2.5;
T = .005;
tmid = (t1+t2)/2; %formula gives to find what t mid is
%--------------------------------------------------------------------------------------------------------%
A = @(t) 1/2*(a2-a1)*tanh(10.*((t-tmid)/((t2-t1))))+(1/2*(a2+a1));
T1 = 0:1:120; %used for plotting x axis
D = @(T1)(p*c.*(A(T1)))/2*m; %drag constant
plot(T1, A(T1), 'b-', 50, .7, 'ro', 70, 50, 'ro') %t1 occurs at 50 seconds in, the area is .7 so I used that as a y co-ordinate and 50 as my x, marking that spot with a red circle.
axis([0 120, .6 70]); 
xlabel('Time')
ylabel('Area')
title('Area over Time')
%--------------------------------------------------------------------------------------------------------%
x(1) = 0;, vx(1) = v0;, y(1) = 0;, vy(1) = 0; %initial variables used to start the loop
for n=1 %initialize time index
    while 1 %forever while loop
        if y(n) > h0, break; end % break when ground is reached
        tn = (n-1)*T; %nth time instant in seconds
        t(n) = tn;  %build time vector, needed for plotting
        Dn = D(n).*(tn); %drag constant in time tn
        v = sqrt(vx(n)^2+vy(n)^2); %problem tells me to write "no need to save V in an array"- not sure what this means
        ax(n) = -Dn * vx(n)*v; %horizontal acceleration
        v(n) = sqrt(vx(n)^2+vy(n)^2); 
        ay(n)= -(D(tn)) * vy(n)*v(n)+g; ; 
        x(n+1) = x(n)+T*vx(n);
        vx(n+1)= vx(n)+T*ax(n);
        y(n+1)=y(n)+T*vy(n);
        vy(n+1)= vy(n)+T*ay(n);
        n = n+1; %updates the index to use N+1, so second round will use 2 for N, as N is defined as 1, N= 1+1, whill use 2 for N in next loop and so on. 
    end 
end
%--------------------------------------------------------------------------------------------------------%
Vc_1 = sqrt((2*m*g)/p*c*A(30));
Vc_2 = sqrt((2*m*g)/p*c*A(80));
Vc_3 = sqrt((2*m*g)/p*c*a1);
Vc_4 = sqrt((2*m*g)/p*c*a2);

[Daniel Martelli]

It did crash, but once i saved the worked it didnt crash

[Image Analyst]

Saving the m-file won't prevent the script from throwing an error. If it's not saved, it will actually ask you to save the file before it runs even the first line of the script. So it can't crash before it's saved. However, we're glad its working (for whatever reason) now.