Changing the variable used in a loop

Hey,

Im trying to write some looping code to make my life easier essentially what I've got is:

tube_inner_R = 0.003

tube_L1=12.14
tube_L2=6.46;
tube_L3=9.84;
tube_L4=8.17;

for inst = 1:4
    
    tube_V=pi*tube_inner_R^2*tube_L(inst);
    
end

What I want is for each time the loop runs it uses the tube_L variable coresponding to that loop to be used to calculate the tube_V for that loop

Im really new to matlab but I have been looking around trying to find an answer and cant find anything that I can make sense of so any help would be appreciated, cheers.

[Stephen23]

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[VBBV]

tube_inner_R = 0.003

tube_inner_R = 0.0030

tube_L=[12.14 6.46 9.84 8.17];  % put them in vector 
 

for inst = 1:4
    
    tube_V(inst)=pi*tube_inner_R^2*tube_L(inst);  % access corresponding element 
    
end
tube_V

tube_V = 1×4

1.0e-03 * 0.3433 0.1827 0.2782 0.2310

[Toby Beisly]

Oh this makes so much more sense than what I was tring to do, thanks for your answer :D

Answer 2

[Steven Lord]

Can you iterate over numbered variables like tube_L1, tube_L2, tube_L3, etc? Yes.

Should you do this? The general consensus is no. See that Answers post for an explanation and alternatives.

In this case, you don't need the loop if you operate on the whole vector at once.

tube_inner_R = 0.003

tube_inner_R = 0.0030

tube_L = [12.14, 6.46, 9.84, 8.17]

tube_L = 1×4

12.1400 6.4600 9.8400 8.1700

tube_V = pi*tube_inner_R^2*tube_L

tube_V = 1×4

1.0e-03 * 0.3433 0.1827 0.2782 0.2310

Wherever you would have used (for example) tube_L3 and tube_V3 (as I'm guessing you would have continued the naming system) instead use tube_L(3) and tube_V(3).

fprintf("For L = %g, V is %g.\n", tube_L(3), tube_V(3))

For L = 9.84, V is 0.000278219.

[Toby Beisly]

Ahh I see having it as one variable makes way more sense now that I think about it, thanks for the help.