[likeshu1103]

t1=(ceil(x/v/dt):N)*dt;
gtx=exp(-a2*x)*a1*x./(2*sqrt(pi*(t1-x/v).^3)).*exp(-(a1*x)^2./(4*(t1-x/v)));
t2=(1:ceil(x/v/dt)-1)*0;
gtx=[t2,gtx];