Array indices must be positive integers or logical values.

Hello,

My code below is displaying the following error message:

"Array indices must be positive integers or logical values.

Error in Assign5_Prob7 (line 38)

phi(i) = atand(tan(phi_o)+((g*t(i))/Vx_o)*((1/3)*((Vx_o/Vx(i)+ sqrt((Vx_o/Vx(i)))+1)))); "

I don't see anything resulting in a zero within the equation. I'm not sure why this error is displaying. Thank you.

Vy_o = 0.00001; 
Vx_o = 2296;
phi_o = atand(Vx_o/Vy_o);

for i = 1:6
    x(i) = (i-1)*200*3;                          
    y(i) = (i-1)*200*3;                          
    Vx(i) = (sqrt(Vx_o) - ((k3/2)*x(i)))^2;   
    t(i) = (x(i)/Vx_o)*sqrt(Vx_o/Vx(i));  
    
    phi(i) = atand(tan(phi_o)+((g*t(i))/Vx_o)*((1/3)*((Vx_o/Vx(i)+ sqrt((Vx_o/Vx(i)))+1)))); 

[Setsuna Yuuki.]

works well for me

Answer 1

[Cris LaPierre]

This error means that your index variable i is either

• negative
• zero
• not an integer

Check your code that you did not include and see if you modify the value of i somewhere before getting to line 38.

[Steven Lord]

Or it could mean that they've created variables named atand, tan, or sqrt that are being referenced instead of the functions by those names that are part of MATLAB being called.

[Jocelyn]

I think the error has something to do with the line directly beneath line 38 (which is the phi(i) =... line).

When I took out the tan(i) = line, the phi(i) = line worked and a table was produced.

Once I put the tan(i) = line back into the code, I got the same message as I posted before:

" Array indices must be positive integers or logical values.

Error in Assign5_Prob7 (line 38)

phi(i) = atand(tan(phi_o)+((g*t(i))/Vx_o)*((1/3)*((Vx_o/Vx(i)+ sqrt((Vx_o/Vx(i)))+1))));

Do you have any thoughts as to why this is happening?

 phi(i) = atand(tan(phi_o)+((g*t(i))/Vx_o)*((1/3)*((Vx_o/Vx(i)+ sqrt((Vx_o/Vx(i)))+1)))); % firing angle 
    
    tan(i)= tan(phi(i))-((g*t(i))/Vx_o)*((1/3)*((Vx_o/Vx(i)+ sqrt((Vx_o/Vx(i)))+1))); % impact angle
  
end

T = table(x(:)/3, x(:), Vx(:), t(:), phi(:), tan(:), 'VariableNames',{'yards', 'feet', 'striking velocity', 'time of flight', 'firing angle', 'impact angle'})

[Cris LaPierre]

The line below 38 will not cause an error to appear in line 38.

Try sharing all 38 lines of your code, rather than just the one or two around the error. If you want, you can attach your script using the paperclip icon.

Answer 2

[Varun Krishna]

t=0:0.01:2;

x(t)=3.*sin(10.*pi.*t).*exp(-2.*t);

[Steven Lord]

There's no such thing as element 0 or element 0.01 of an array in MATLAB. Replace x(t) with just x. Or if you want to create a function that can be evaluated for different values of t, make x an anonymous function.

t=0:0.01:2;
x=3.*sin(10.*pi.*t).*exp(-2.*t);
y = @(t) 3.*sin(10.*pi.*t).*exp(-2.*t);
isequal(x, y(t)) % evaluate y at the points in t

ans = logical
   1