How to evaluate the following equation with Ei function?

Hey, guys

I am having trouble in evaluation of the following equation: rd=r/rw, td=k*t/(phi*mu*c*rw^2), pd=((2*pi*k*h)/(q*B*mu)*(IP-p(r,t))

pd(rd,td)=-1/2*Ei*(-rd^2/4*td)> the following equation needs to be evaluated

t=3000000 nr=nx=161 (to be introduced instead of r) q=0.02 k=5e-13 mu=0.00035 c=1.5e-8 phi=0.25 rw=0.1 h=4.5 B=1.1

My code is below: st=size(t) nr=nx;

if true
  % for i=1:1:st(1)
    rd=r(1:nr)/wb
    td=0.0036*k*t(i)/(phi*mu*c*wb^2)
    pd=((pi*h*k)/(1.842*q*1.1*mu))*(IP-p(i,1:nr))
    Ei_from_mfun=mfun('Ei',1,-rd^2/(4*td))
    pd=1/2*Ei_from_mfun
    plot(time,pd,'bo')
end
end

The following command appears: if true % ??? Index exceeds matrix dimensions. Error in ==> radialflow1 at 103 pd=((pi*h*k)/(1.842*q*1.1*mu))*(IP-p(i,1:nr))

end
Can you please help to fix the problem for every time, t and pressure,p?

Thanks