Numerical Integration problem

Hi can anyone advise: I am trying to integrate numerically an equation from z_star_=25 down to d=4. However, the solution derives NaN at 6 down to 4.... The code/equation:

d=4;
z_star=25;  
u_star_z_star=0.5;    
k=0.4;

F = @(x)(((sin((pi()/2)*((x-d)/(z_star-d))).^1.28).^0.333)./(x-d))*(u_star_z_star/k);

%%%--- TABULATING SOLUTION BETWEEN LIMITS --- %%%
A=zeros(85,2);
a=1;
b=1;
z=z_star
for z=z:-0.25:d;
Q(a) = quadv(F,d,z); 

D(b)=z
a=a+1;
b=b+1
end

for i=1:length(A);

A(i,1)=D(i);
A(i,2)=Q(i);
end

Answer 1

[Andrei Bobrov]

use quadgk

for quadgk(F,d,z), if z = 4 then F(4) = NaN, division by zero.