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发表于 2004-7-22 10:49:22
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2.构造判断矩阵<></P>
构造判断矩阵是进行层次分析的关键。<></P>
设有<I normal">n</I>个因素(准则)<I normal">C</I><SUB>1</SUB>,<I normal">C</I><SUB>2</SUB>,…,<I normal">C<SUB>n</SUB></I>对总目标<I normal">G</I>有影响,要确定它们在<I normal">G</I>中的比重。采用成对比较法,即每次取两个因素<I normal">c<SUB>i</SUB></I>和<I normal">c<SUB>j</SUB></I>,用<I normal">a<SUB>ij</SUB></I>表示<I normal">c<SUB>i</SUB></I>与<I normal">c<SUB>j</SUB></I>对<I normal">G</I>影响之比。譬如本例中<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image009.gif"> </SUB>与<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image011.gif"> </SUB>之比设定为1:5,与<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image013.gif"> </SUB>之比为1:3,<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image015.gif"> </SUB>=3:1。将全部比较的结果用矩阵<></P>
<EM> A</EM>=(<I normal">a<SUB>ij</SUB></I>)<I normal"><SUB>n</SUB></I><SUB>×<I normal">n</I></SUB> (<I normal">a<SUB>ij</SUB></I>>0)<P></P>
表示。则<B><I normal"> </I></B><I normal">A</I>是正互反阵,因为<P></P>
<I normal"> a<SUB>ii</SUB></I>=1,<I normal">a<SUB>ji</SUB></I>=1/<I normal">a<SUB>ij</SUB></I> (<I normal">i</I>,<I normal">j</I>=1,2,…,<I normal">n</I>)。<P></P>
如何确定<I normal">a<SUB>ij</SUB></I>的值,人们常取数字1~9及其倒数作为<I normal">a<SUB>ij</SUB></I>的取值范围。这是因为在进行定性成对比较时,人们头脑中的5个明显等级可数量化为如表6-1所示。在每两个等级之间各有一个中间状态,依次用2,4,6,8将其量化。
表6-1 因素等级<TABLE medium none; BORDER-TOP: medium none; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellSpacing=0 cellPadding=0 align=center border=1><TR><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; 52: " ="70"><P><I normal">c<SUB>i</SUB></I>比<I normal">c<SUB>j</SUB></I><P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; 52: " ="70"><P>相同<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; 52: " ="70"><P>稍强<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; 52: " ="70"><P>强<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; 52: " ="70"><P>很强<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; 52: " ="70"><P>绝对强<P></P></P></TD></TR><TR><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt; 52: " ="70"><P><I normal">a<SUB>ij</SUB></I><P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; 52: " ="70"><P>1<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; 52: " ="70"><P>3<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; 52: " ="70"><P>5<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; 52: " ="70"><P>7<P></P></P></TD><TD windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; 52: " ="70"><P>9<P></P></P></TD></TR></TABLE><P> 于是本问题的判断矩阵<I normal">G</I>-<I normal">C</I>构造为<P></P>
<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image017.gif"> </SUB><P></P>
再分别构造判断矩阵<I normal">C</I><SUB>1</SUB>-<I normal">P</I>,<I normal">C</I><SUB>2</SUB>-<I normal">P</I>,<I normal">C</I><SUB>3</SUB>-<I normal">P</I>,不妨设定为<P></P></P><P><SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image019.gif"> </SUB>, <SUB><img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image021.gif"> </SUB>, <SUB><img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image023.gif"> </SUB>。<P></P>
仔细分析上述成对比较矩阵<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image025.gif"> </SUB>可以发现,既然<SUB>
<img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image027.gif"> </SUB>应该是<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image029.gif"> </SUB>而不是<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image031.gif"> </SUB>,才能说明这个成对比较是一致的。使用数学语言即,对三个因素x<I normal"><SUB>i</SUB></I>,x<I normal"><SUB>j</SUB></I>,x<SUB>k</SUB>进行两两比较:由x<I normal"><SUB>i</SUB></I>与x<I normal"><SUB>j</SUB></I>相比得到<I normal">a<SUB>ij</SUB></I>,由<I>x<SUB>j</SUB></I>与<I>x<SUB>k</SUB></I>相比得到<I normal">a<SUB>j</SUB></I><SUB>k</SUB>,再由<I>x</I><I normal"><SUB>i</SUB></I>与x<SUB>k</SUB>相比得到<I normal">a<SUB>i</SUB></I><SUB>k</SUB>,则应有<I normal">a<SUB>ij</SUB>a<SUB>j</SUB></I><SUB>k</SUB>=<I normal">a<SUB>i</SUB></I><SUB>k</SUB>,但完全可能出现<I normal">a<SUB>ij</SUB>a<SUB>j</SUB></I><SUB>k</SUB>≠<I normal">a<SUB>i</SUB></I><SUB>k</SUB>。<P></P>
由于人们要做众多因素比较,全部一致的要求是太苛刻了。因此,我们给出在成对比较不一致的情况下计算各因素对上一因素的权重的方法,并且确定这种不一致的容许范围。自然,此前进行相应矩阵的一致性检验是必须的。<P></P>
所谓一个正互反矩阵A为一致性的,是指其元素满足<I normal">a<SUB>ij</SUB>a<SUB>j</SUB></I><SUB>k</SUB>=<I normal">a<SUB>i</SUB></I><SUB>k</SUB>,<I normal">i,j,k</I> =1,2,…<I normal">n</I>。我们还有<P></P>
引理 正互反阵的最大特征根是单根且是正实数,对应着正的特征向量。<P></P>
定理 <I normal">n</I>阶正互反矩阵<I normal">A</I>=(<I normal">a<SUB>ij</SUB></I>)<I normal"><SUB>n</SUB></I><SUB>×<I normal">n</I></SUB>是一致阵当且仅当<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image033.gif"> </SUB>=<I normal">n</I><I normal">,</I><P></P>其中<SUB> <img src="http://202.205.160.49:8080/media_file/rm/ip3/zhangxh/2004_03_01/sxjm_28/htm/sxjm_28.files/image035.gif"> </SUB>是A的最大特征值<P></P></P> |
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