📄 第四节 用mathematica解方程和作级数运算.htm
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<P class=MsoNormal style="line-height: 200%"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><b><font size="4">(</font></b></SPAN><b><font size="4"><SPAN
lang=EN-US>6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">)</SPAN><SPAN
lang=EN-US>In[9]:=Solve[{x^2 + y^2 + 4x - 2y + 3 = = 0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> x^2 + 4x*y - y^2 + 10y - 9 = = 0}</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> {x</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> y}]</SPAN></font></b></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><SPAN lang=EN-US><font size="4"><b>Out[9]=<SPAN
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<P class=MsoNormal style="line-height: 200%"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><b><font size="4">(</font></b></SPAN><b><font size="4"><SPAN
lang=EN-US>7</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">)</SPAN><SPAN
lang=EN-US> In[10]:=Solve[{x1 + x2 + x3 + x4 + x5 = = 0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> 3x1 + 2x2 + x3 + x4 - 3x5 = = 0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN>
<SPAN lang=EN-US>x2 + 2x3 + 2x4 + 6x5 = = 0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> 5x1 + 4x2 + 3x3 + 3x4 - x5 = = 0}</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> {x1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> x2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> x3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN>
<SPAN lang=EN-US>x4</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> x5}]</SPAN></font></b></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><font size="4"><b><SPAN
lang=EN-US>Solve</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">::</SPAN><SPAN
lang=EN-US>svars</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">:</SPAN><SPAN
lang=EN-US>Equations may not give solutions for all "solve"</SPAN></b></font></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><SPAN
lang=EN-US><font size="4"><b>variables.</b></font></SPAN></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><font size="4"><b><SPAN lang=EN-US>Out[10]={{x1
-> x3 + x4 + 5 x5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US> x2 -> -2 x3 - 2 x4 - 6 x5}}</SPAN></b></font></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><font size="4"><b>上述结果表明,虽然方程组不能给出具体解,但仍会给出方程组的一般解。</b></font></SPAN></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"> </P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"> </P>
<P class=MsoNormal style="line-height: 200%"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><b><font color="#FF0000" size="5">二、<a name="常微分方程">常微分方程</a></font></b></SPAN></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><font size="4"><b><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">解常微分方程实际上就是求满足方程的某函数</SPAN><SPAN
lang=EN-US>y[x]</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">。在</SPAN><SPAN
lang=EN-US>Mathematica4.0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">中,其导数用</SPAN><SPAN
lang=EN-US>y’[x]</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">、</SPAN><SPAN
lang=EN-US>y’’[x]</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">等来表示。</SPAN></b></font></P>
<P class=MsoNormal style="text-indent: 17.95pt; line-height: 200%"><font size="4"><b><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">求解常微分方程主要由函数</SPAN><SPAN
lang=EN-US>DSolve</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">来完成。以下给出其使用格式:</SPAN></b></font></P>
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style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><font size="4"><b>格式</b></font></SPAN></P></TD>
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style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><font size="4"><b>含义</b></font></SPAN></P></TD></TR>
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<P class=MsoNormal style="line-height: 200%"><SPAN lang=EN-US><b><font size="4">DSolve[eqns</font></b></SPAN><b><font size="4"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US>y[x]</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US>x]</SPAN></font></b></P></TD>
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<P class=MsoNormal style="line-height: 200%"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><b><font size="4">求解微分方程</font></b></SPAN><b><font size="4"><SPAN
lang=EN-US>eqns</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,其中</SPAN><SPAN
lang=EN-US>y[x]</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">为</SPAN><SPAN
lang=EN-US>x</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">的函数</SPAN></font></b></P></TD></TR>
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<P class=MsoNormal style="line-height: 200%"><SPAN lang=EN-US><b><font size="4">DSolve[eqns</font></b></SPAN><b><font size="4"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US>y</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,</SPAN><SPAN
lang=EN-US>x]</SPAN></font></b></P></TD>
<TD
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<P class=MsoNormal style="line-height: 200%"><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'"><b><font size="4">求解微分方程</font></b></SPAN><b><font size="4"><SPAN
lang=EN-US>eqns</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">,其中</SPAN><SPAN
lang=EN-US>y[x]</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">为</SPAN><SPAN
lang=EN-US>x</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">的函数</SPAN></font></b></P></TD></TR>
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