[求助]用null 解线性齐次方程组 出错
<P>偶 刚学习matlab，现在遇到了一个小问题。<br>用 null 解线性齐次方程组时，总是得零解呢?系数矩阵是正定的阿！<br>例如<br>e =</P><P>-13.8063 13.8063<br> 41.4189-41.4189<br><br>>> null(e,'r')</P>
<P>ans =</P>
<P> Empty matrix: 2-by-0<br><br>但是明明应该有解的阿。哪位大虾给指点一下。问题出在哪里了阿？<br><br>还有，null(a,'r') 和 null(a)有什么区别阿？<br></P>
[此贴子已经被作者于2006-4-5 10:30:19编辑过]
回复：（lynette100）[求助]用null 解线性齐次方程组 ...
帮助里不是有吗？自己看吧doc null<BR> <P><BR>Syntax<BR>Z = null(A)<BR>Z = null(A,'r')</P><P>Description</P>
<P>Z = null(A) is an orthonormal basis for the null space of A obtained from the singular value decomposition. That is, A*Z has negligible elements, size(Z,2) is the nullity of A, and Z'*Z = I. <BR><BR>Z = null(A,'r') is a "rational" basis for the null space obtained from the reduced row echelon form. A*Z is zero, size(Z,2) is an estimate for the nullity of A, and, if A is a small matrix with integer elements, the elements of the reduced row echelon form (as computed using rref) are ratios of small integers. <BR>The orthonormal basis is preferable numerically, while the rational basis may be preferable pedagogically.<BR>不过我英文不好，大概明白...<BR>多多学习才是，哎，<BR>我麻时候能成为高手呢<BR>快了快了<BR>就在今天...<BR><BR>不过弱问，2-by-0是什么意思呢？2行2列全是0？</P>
回复：（lynette100）[求助]用null 解线性齐次方程组 ...
<P>2-by-0表示2*0的矩阵</P> 恩，看的有点晕，矩阵的知识都忘光了<BR><BR>现在关键是，不知道自己那样哪里出错了<BR>还望高手指点一二阿
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