Help！ 三维以上的累计正态分布函数概率怎么算啊？

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<>help! 三维以上的累计正态分布函数概率怎么用啊？我怎么试了半天总是不对？</P>
<>即下面的函数：</P>
<><a href="http://documents.wolfram.com/v4/AddOns/StandardPackages/Statistics/ContinuousDistributions.html" target="_blank" ><TT>CDF</TT></A>[<TT>MultinormalDistribution</TT>[<I>mu</I>, <I>sigma</I>], <I>range]</I></P>
<P><EM>CDF[MultinormalDistribution[{0, 0, 0}, {{1, 0.5, 0.7}, {0.5, 1, 0.9}, {0.7,
    0.9, 1}}], {0, 0, 0}] </EM></P>
<P><EM>CDF::mnormsig: The parameter sigma in MultinormalDistribution[mu, sigma] does \
not have a structure allowing computation of CDF[MultinormalDistribution[mu, \
sigma], x].   Currently, the structure of sigma is restricted to  {{s1^2,   \
s1 s2 l1 l2,   s1 s3 l1 l3,   ...}, {s2 s1 l2 l1,   s2^2,   s2 s3 l2 l3,   \
...}, {s3 s1 l3 l1,   s3 s2 l3 l2,   s3^2,   ...},   ...}, where Abs[li] &lt;= \
1, i = 1, 2, 3, ... .</EM></P>
<P><EM>上面的说明怎么会事，我怎么看不懂， 帮助里也没有。</EM></P>
<P><EM></EM> </P>