Convert 1x1 sym to float - matlab

Question

I attempt to convert a 1x1 sym to float in the program below below but it fails. Why?
The culprit line:
sol = ode45(M,[30 45],[double(H0) double(V0)]);
The error message:
Error using odearguments (line 111) Inputs must be floats, namely
single or double.
Error in ode45 (line 114) [neq, tspan, ntspan, next, t0, tfinal, tdir,
y0, f0, odeArgs, odeFcn, ...
Error in extra_credit_HW5_ME70 (line 60) sol = ode45(M,[30
45],[subs(H0) subs(V0)]);
The code:
clc;
clear all;
close all;
%This program solves the rocket program by using a system of second order
%differential which I derived (see Homework 5)
%code explanation from http://www.mathworks.com/products/symbolic/code-examples.html? file=/products/demos/symbolictlbx/second_order_differential_equation/solve-a-second-order-differential-equation.html
Ve=3500;
Mo=400;
Me=5;
g=9.81;
Cd=.5;
Af=.2;
R=287
T=273.15;
Patm=101325;
syms y(t);
%Note: From the hw: "Take the density of air at sea level to be 1.21
%kg/m3." I decided to model the density with an exponential function p(h)=(Patm*exp(-g*y/(R*T))/(R*T))
V = odeToVectorField(diff(y, 2) == Ve*Me/(Mo-Me.*t)-g-.5*Cd* (Patm*exp(-g*y/(R*T))/(R*T)) *diff(y).^2*Af/(Mo-Me.*t));
M = matlabFunction(V,'vars', {'t','Y'});
sol = ode45(M,[0 30],[0 0]);
x = linspace(0,30,250);
y = deval(sol,x,1);
plot(x,y);
% legend('No air resistance, air resistance');
hold on;
Mo=350;
syms y(t);
%Initial conditions for case where mass is dumped.
H0=y(end);
V0=( (y(end)-y(end-1)) / (x(end)-x(end-1)) );
%Note: From the hw: "Take the density of air at sea level to be 1.21
%kg/m3." I decided to model the density with an exponential function p(h)=(Patm*exp(-g*y/(R*T))/(R*T))
V = odeToVectorField(diff(y, 2) == Ve*Me/(Mo-Me.*t)-g-.5*Cd* (Patm*exp(-g*y/(R*T))/(R*T)) *diff(y).^2*Af/(Mo-Me.*t));
M = matlabFunction(V,'vars', {'t','Y'});
sol = ode45(M,[30 45],[double(H0) double(V0)]);
x = linspace(30,45,500);
y = deval(sol,x,1);
plot(x,y,'cyan');
% legend('No air resistance, air resistance');
title('Rocket height versus time for stages launch')
xlabel('time (seconds)')
ylabel('height (meters)')