< 0cm 0cm 0pt">解2:<p></p></P>< 0cm 0cm 0pt; TEXT-INDENT: 21pt">在<FONT face="Times New Roman">x-y</FONT>平面上画散点图,直观地知道<FONT face="Times New Roman">y</FONT>与<FONT face="Times New Roman">x</FONT>大致为二次函数关系。</P>< 0cm 0cm 0pt; TEXT-INDENT: 21pt">设模型为<FONT face="Times New Roman">y=a<SUB>1</SUB>x<SUP>2</SUP>+a<SUB>2</SUB>x+a<SUB>3<p></p></SUB></FONT></P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt">此问题可以利用命令<FONT face="Times New Roman">polyfit(x,y,2)</FONT>来解,也可以象上题一样求解。下面介绍用命令<FONT face="Times New Roman">polytool</FONT>来解。</P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt">首先在命令窗口键入</P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT face="Times New Roman">x=17:2:29;x=[x,x];</FONT></P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT face="Times New Roman">y=[20.48,25.13,26.15 30,26.1,20.3,19.35,24.35,28.11,26.3,31.4,26.92,25.7,21.3];</FONT></P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT face="Times New Roman">polytool</FONT>(<FONT face="Times New Roman">x,y,2</FONT>)</P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt">得到一个交互式窗口</P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> <p></p></FONT></P><P 0cm 0cm 0pt"><v:shapetype><v:stroke joinstyle="miter"></v:stroke><v:formulas><v:f eqn="if lineDrawn pixelLineWidth 0"></v:f><v:f eqn="sum @0 1 0"></v:f><v:f eqn="sum 0 0 @1"></v:f><v:f eqn="prod @2 1 2"></v:f><v:f eqn="prod @3 21600 pixelWidth"></v:f><v:f eqn="prod @3 21600 pixelHeight"></v:f><v:f eqn="sum @0 0 1"></v:f><v:f eqn="prod @6 1 2"></v:f><v:f eqn="prod @7 21600 pixelWidth"></v:f><v:f eqn="sum @8 21600 0"></v:f><v:f eqn="prod @7 21600 pixelHeight"></v:f><v:f eqn="sum @10 21600 0"></v:f></v:formulas><v:path gradientshapeok="t" connecttype="rect" extrusionok="f"></v:path><lock v:ext="edit" aspectratio="t"></lock></v:shapetype><v:shape><v:imagedata><FONT face="Times New Roman"></FONT></v:imagedata></v:shape></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> <p></p></FONT></P><P 0cm 0cm 0pt">窗口中绿线为拟合曲线、红线为<FONT face="Times New Roman">y</FONT>的置信区间、可通过移动鼠标的十字线或通过在窗口下方输入来设定<FONT face="Times New Roman">x</FONT>值,窗口左边则输出与<FONT face="Times New Roman">x</FONT>对应的<FONT face="Times New Roman">y</FONT>值及<FONT face="Times New Roman">y</FONT>的置信区间。通过左下方的<FONT face="Times New Roman">Export</FONT>下拉菜单可输出回归系数等。更详细的解释可通过<FONT face="Times New Roman">help</FONT>查阅。</P><P 0cm 0cm 0pt">解<FONT face="Times New Roman">3.</FONT>这是一个多元回归问题。若设回归模型是线性的,即设<FONT face="Times New Roman">y=</FONT>β<SUB>0</SUB>+β<SUB>1</SUB>x<SUB>1</SUB>+β<SUB>2</SUB>x<SUB>2</SUB></P><P 0cm 0cm 0pt">那么依然用<FONT face="Times New Roman">regress(y,x,alpha)</FONT>求回归系数。键入</P><P 0cm 0cm 0pt"><FONT face="Times New Roman">x1=[120,140,190,130,155,175,125,145,180,150];</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman">x2=[100,110,90,150,210,150,250,270,300,250];</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman">y=[102,100,120,77,46,93,26,69,65,85]';</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman">x=[ones(10,1),x1',x2'];</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman">[b,bint,r,rint,stats]=regress(y,x);b,bint,stats,</FONT></P><P 0cm 0cm 0pt">得</P><P 0cm 0cm 0pt"><FONT face="Times New Roman">b =</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> 66.5176</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> 0.4139</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> -0.2698</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman">bint =</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> -32.5060 165.5411</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> -0.2018 1.0296</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman"> -0.4611 -0.0785</FONT></P><P 0cm 0cm 0pt"><FONT face="Times New Roman">stats =</FONT></P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT face="Times New Roman">0.6527 6.5786 0.0247</FONT></P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt"><FONT face="Times New Roman">p=0.0247,</FONT>若显著水平取<FONT face="Times New Roman">0,01</FONT>,则模型不能用;<FONT face="Times New Roman">R2=0.6527</FONT>较小<FONT face="Times New Roman">;</FONT>β<SUB>0</SUB>,β<SUB>1</SUB>的置信区间包含零点。因此结果不理想。于是设模型为二次函数。此题设模型为纯二次函数:<p></p></P><P 0cm 0cm 0pt; TEXT-INDENT: 21pt; TEXT-ALIGN: center" align=center>y=β<SUB>0</SUB>+β<SUB>1</SUB>x<SUB>1</SUB>+β<SUB>2</SUB>x<SUB>2</SUB>+β<SUB>11</SUB>x<SUB>1</SUB><SUP>2</SUP>+β<SUB>22</SUB>x<SUB>2</SUB><SUP>2</SUP><p></p></P> |