solving a multiple variable equation with variables that increment

So my program is an attempt to create a simple wind tunnel simulator to test different projectiles. here is the script:

function answer = efficiency()

syms V C A

%% Drag force equation = (1/2)pV^2CA

    %p = density of air = 0.00128 g/mL
    %V = velocity = variable V
    %C = Coefficient of drag = variable C
    %A = Cross sectional area = function A
    %F = 0.5 * 0.00128(g/mL) * V^2(m/s^2) * C * A(m)

    %%Drag Coefficient
    % Drag Coefficient of Sphere = 0.47  
    % Drag Coefficient of cone = 0.50     
    % Drag Coefficient of cube = 1.05             
    % Drag Coefficient of long cylinder = 0.82  

    % Selection of projectile shape

        X = menu('projectile shape','sphere','cone','cube','cylinder','main menu');
        if X == 1
            C = 0.47;
        elseif X == 2
            C = 0.50;
        elseif X == 3
            C = 1.05;
        elseif X == 4
            C = 0.82;
        elseif X ==5
            C = WindTunnel(); 
        end
%%Cross sectional area
    % area of sphere = pi r^2
    % area of cone = pi r^2
    % area of cube = base * height
    % area of long cylinder = pi r^2 

            for A = .1:.1:1 
            end
            for V = 100:100:1000       
            end 

    answer = solve(.00064*C*A*V^2);
        answer =
end

It is only outputing zeros for the solutions any help would be appreciated

Answer 1

[Star Strider]

I haven’t run your code, but two problems are immediately apparent:

First, these two lines will simply loop without doing anything, and return the last value of A and V respectively:

            for A = .1:.1:1 
            end
            for V = 100:100:1000       
            end

Second in this line:

answer = solve(.00064*C*A*V^2);

what are you solving for?

If you want ‘answer’ to be the result of that calculation, simply do:

answer = .00064*C*A*V^2;

If you want it for every value of A and V, you have to put it into nested loops and index it.

For example:

A = .1:.1:1;
V = 100:100:1000;
for k1 = 1:length(A)
    for k2 = 1:length(V)
        answer(k1,k2) = 0.00064*C*A(k1)*V(k2)^2;
    end
end

Make necessary changes so it does what you want.

A third observation is that you don’t need to call the Symbolic Math Toolbox at all. It is not well-suited to iterative calculations, and you’re not doing anything with it.

The last line in your code is simply ‘answer =’. I assume that’s a typo in typing your Question, because it would throw an error at compilation and your code wouldn’t calculate anything.

[Andrew Lheureux]

Awesome, that helped out perfectly. thank you very much

[Star Strider]

My pleasure!