MATLAB: Below is the code and I get the corresponding error message. I’m trying to use fzero on the function defined below. What am I doing wrong

fzeroMATLAB

function [ y ] = mainFunc( v )
d = 0.15; % Diameter of sphere, meters
g = 9.8; % acceleration due to gravitym m/s^2
m = 0.5; % mass of sphere in kg
P = 101300; % N/m^2
R = 287; %gas cosntant
% Viscosisty constants b1 = 2.156954157e-14;
b2 = -5.332634033e-11;
b3 = 7.477905983e-8;
b4 = 2.527878788e-7;
T = linspace(213,333, 241); %temp in Kelvin
rho = 0*T;
u = 0*T;
for i = 1:length(T)
    u(i) = b1*T(i)^3 + b2*T(i)^2 + b3*T(i) + b4;
end
for i = 1:length(T)
    rho(i) = P / (R*T(i));
end
y = (24./(rho.*v*d./u) + 6./(1 + sqrt.(rho.*v*d./u)) + 0.4 – m*g) * (1/2) .* rho * v^2 * ((pi*d^2)/4) ;
end
ERROR MESSAGE >
 HW5
Error using fzero (line 289)
FZERO cannot continue because user supplied function_handle ==> mainFunc failed with the error below.
 Argument to dynamic structure reference must evaluate to a valid field name.
Error in HW5 (line 3) z = fzero(fun,x0)

Best Answer

Good start, but what you failed to show is how you called the blasted thing! Insufficient information.
Oh, and b1 is undefined, because you left it in a comment. My guess is that was done when you posted the function here though.
(You should learn to use the debugger!)
As it turns out though, the answer is simple. It seems like you think that a period should be placed in somewhat random places. For example, some of the multiplies are done using . but most of them with . but not all. I won't check that those always ended up as scalar operations, but I have a funny feeling they are not. That could be dangerous, although it was not the cause of your immediate problem.
y = (24./(rho.*v*d./u) + 6./(1 + sqrt.(rho.*v*d./u)) + 0.4 - m*g) * (1/2) .* rho * v^2 * ((pi*d^2)/4) ;
The problem? sqrt should NOT have a . after it.
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