Array indices must be positive integers

I'm trying to use the midpoint formula to compute the value of the integral, but it keeps showing the error message "Array indices must be positive integrs or logical values." I don't know how to solve it. Thanks!

Answer 1

[Steven Lord]

The variable func is a vector, the value of the function handle f evaluated at the points in x. On the line where you compute mid_val you're indexing into that vector with values that likely aren't integer values. Were you trying to evalate the function handle f at those points? If so use f instead of func on that line.

Answer 2

[VBBV]

assign the func to f inside the custom function as below , probably you mean this

f = @(x) x.^3.*exp(-x.^3);
a = 0; b = 10; n = 100;
mid_val = integral_mid(f,a,b,n)

mid_val = 0.2977

function mid_val = integral_mid(f,a,b,n)
h = (b-a)/n;
%x = a:h:b;
% assign the func to f 
func = f;
xmid = (a+h/2):h:b;
mid_val = h*sum(func(xmid));
end