Using the shooting method with ode45 and lagr

Im getting an error while trying to apply the shooting method and I cant get it to work if someone could help

Here is the main part of the code:

clc
clear all
close all

 m = 1;
 K = 1;
 B=0.5;
 y0=2.0;
 v0=0;
 tfin=70;
 h=0.01;
 t=0:h:tfin;
 y(1)=y0;
 v(1)=v0;
 Amp=-2;
 u=[2.5 2.6] 
 
tol_shot=1e-10;  
reltol=3e-14;
abstol=1e-13;
abstol_1=abstol;
abstol_2=abstol;
options=odeset('RelTol',reltol,'AbsTol',[abstol_1 abstol_2]);

i=1;
dif=1; 
while tol_shot< dif

 f1=@(T,YV) [YV(2);(u(i)*(1-YV(2)^2)*YV(2) - K*(B*YV(1)^2))/m];

[t,yv]=ode45(f1,t,[y0,v0],options);
y=yv(:,1);
v=yv(:,2);



%------------ Shooting
ind=find(y==min(y),1); 

aux=lagr(t(ind-1:ind+1),-y(ind-1:ind+1)); % lagr is a lagrange function, input coodenates in wich we want to find the max, output ind of the max point
Aneg(i)=-aux(2);
dif=abs(Aneg(i)-Amp);
    if i>1
        m=(Aneg(i)-Aneg(i-1))/(u(i)-u(i-1));
        u(i+1)=u(i)-(Aneg(i)-Amp)/m;
    end
    
    plot(t,y)
    title(['u=',num2str(u(i)), '    Amp neg=' ,num2str(Aneg(i))])

i=i+1;

   clear y v aux ind aneg 
end

u(end-1)

the error im getting is this one:

Warning: Failure at t=1.620779e-01.  Unable to meet integration tolerances without reducing the step size below the smallest value
allowed (4.440892e-16) at time t. 
> In ode45 (line 360)
  In shooting (line 39) 
Array indices must be positive integers or logical values.

Error in shooting (line 49)
aux=lagr(t(ind-1:ind+1),-y(ind-1:ind+1));