[MATLAB基础] 一个基础的程序问题。。

[inuyasha]

=======================原程序======================
function shiyan3
syms x
R=6378;h=600;
H=[51000 71000 128000 370000];
T=[16 24 48 116]*3600;
for i=1:4
a=(h+H(i)+2*R)/2;
c=(H(i)-h)/2;
b=sqrt(a^2-c^2);
f=sqrt(a^2*(sin(x))*2+b^2*(cos(x))^2);
l(i)=2*int(f,x,0,pi);
L(i)=double(l(i));
V(i)=L(i)/T(i);
end
L
V

==========================运行结果========================
Warning: Explicit integral could not be found.
> In sym.int at 64
In shiyan3 at 11
Warning: Explicit integral could not be found.
> In sym.int at 64
In shiyan3 at 11
Warning: Explicit integral could not be found.
> In sym.int at 64
In shiyan3 at 11
Warning: Explicit integral could not be found.
> In sym.int at 64
In shiyan3 at 11

L =

1.0e+006 *

0.2408 0.3099 0.5054 1.3286


V =

4.1798 3.5872 2.9246 3.1815

=========================我的问题====================
我用的2009a版的MATLAB。。。
那个warning 所指的问题是什么啊。。。程序应该改哪些部分。。。
谢谢了，，大家。。