da=0.1 ; 
I=[] ; % it contains nothing 
aa=[ 0:da:1 ]; 
N=length(aa) ;
I=zeros(1,N) ; 
j=0; 
for a = 0:da:1
    j=j+1 ; 
N=10; 
L=1; 
dx=L/N; 
x=[ dx/2: dx :1-dx/2];
f=a*x.^2;
Integral=sum(f)*dx;
I(j)=Integral;
end


figure
plot( [ 0:da:1 ],I )