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[编程进阶] 求助，请高手看下下面两个程序是怎么回事？谢谢！！！！

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xiaomaoxiaomao
发表于 2011-11-30 15:35:26 | 显示全部楼层 |阅读模式 来自 河南郑州
程序1：
x = {1, 2};
a = 3.1137681326839752 I;
Abs[x + (1 + a)^2 - (1 + 2 a)^0.5]
程序2：
d = {{1, 10.650871207105963}, {2, 9.758434568400363}};
FindFit[d, {Abs[
   b + (1 + c I)^2 + (1 + 2 c I)^0.5], {Im[c] == 0}}, {c}, b]
请问下，为啥下面拟合程序为啥得不到原来解出来的数值呀？？谢谢了！！！！！！！！！！
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guocong89
发表于 2011-12-1 14:55:06 | 显示全部楼层 来自 北京
Simdroid开发平台
你总共就两个样本点,插值函数自然有可能很不同
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xiaomaoxiaomao
 楼主| 发表于 2011-12-2 15:19:58 | 显示全部楼层 来自 河南郑州
guocong89 发表于 2011-12-1 14:55
你总共就两个样本点,插值函数自然有可能很不同

先谢谢楼主，这个方程的拟合，是不是数据点越多，拟合到的结果越精确？
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xiaomaoxiaomao
 楼主| 发表于 2011-12-2 16:06:30 | 显示全部楼层 来自 河南郑州
guocong89 发表于 2011-12-1 14:55
你总共就两个样本点,插值函数自然有可能很不同

您能帮我指点下这两个程序：请问一下，下边这两个程序的差别：
程序1：\[Eta] = 1;
\[Omega] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
\[Gamma] = 2;
p = N[(1/(Pi*\[Omega]*4*\[Eta]^2))*(Im[
      I/\[Eta] -
       Sqrt[1 + \[Omega]*
          I/\[Eta]]]/(Abs[\[Gamma]/(4*\[Eta]^2) + (1 + \[Omega]*
             I/(2*\[Eta]))^2 - Sqrt[1 + \[Omega]*I/\[Eta]]])^2)]
结果：{0.135583, 0.00411162, -0.000121982, -0.000203706, -0.000125044, \
-0.0000733538, -0.0000443117, -0.0000278519, -0.0000181852, \
-0.0000122836}
程序2：data = {{1, 0.1355827927262082}, {2,
    0.004111621860777021}, {3, -0.00012198235102687155}, {4, \
-0.00020370574572352768}, {5, -0.0001250438976608526}, {6, \
-0.00007335379189862897}, {7, -0.00004431170043888969}, {8, \
-0.00002785194241379399}, {9, -0.000018185153639455487}, {10, \
-0.000012283648257132023}};
FindFit[data, {(1/(Pi*c*4*a^2))*(Im[
      I/a - Sqrt[1 + c*I/a]]/(Abs[
        b/(4*a^2) + (1 + c*I/(2*a))^2 - Sqrt[1 + c*I/a]])^2),
  Im[a] == 0, Im == 0}, {a, b}, c]
结果：{a -> 1.04837, b -> 0.990768}
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guocong89
发表于 2011-12-4 14:49:36 | 显示全部楼层 来自 北京
本帖最后由 guocong89 于 2011-12-4 14:51 编辑
xiaomaoxiaomao 发表于 2011-12-2 16:06
您能帮我指点下这两个程序：请问一下，下边这两个程序的差别：
程序1：\[Eta] = 1;
\[Omega] = {1, 2, 3, ...

这个拟合结果并非不好啊
  1. Show[ListPlot[data, PlotStyle -> {Red, PointSize[Large]}],
  2. Plot[f /. res, {c, 1, 10}]]
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xiaomaoxiaomao
 楼主| 发表于 2011-12-7 09:44:10 | 显示全部楼层 来自 河南郑州
guocong89 发表于 2011-12-4 14:49
这个拟合结果并非不好啊

:victory:谢谢斑竹
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xiaomaoxiaomao
 楼主| 发表于 2011-12-7 11:52:46 | 显示全部楼层 来自 河南郑州
guocong89 发表于 2011-12-4 14:49
这个拟合结果并非不好啊

版主，你能帮我看下下面的这个程序吗！！跟前面的形式是相同的，可是拟合出来的效果却是不尽人意，希望版主能帮忙看下！！谢谢了
\[Tau] = \[Rho]/(2*\[Eta]*q^2);
y = \[Gamma]*\[Rho]/(4*q*\[Eta]^2);
t = 302.3;
k = 1.3806505*10^(-23);
\[Rho] = 781.28;
q = 63157.69;
data = {{10125, 0.002650000}, {10200, 0.002690000}, {10275,
    0.002720000}, {10350, 0.002760000}, {10425, 0.002810000}, {10500,
    0.002850000}, {10575, 0.002890000}, {10650, 0.002940000}, {10725,
    0.002980000}, {10800, 0.003030000}, {10875, 0.003080000}, {10950,
    0.003120000}, {11025, 0.003170000}, {11100, 0.003220000}, {11175,
    0.003260000}, {11250, 0.003310000}, {11325, 0.003350000}, {11400,
    0.003390000}, {11475, 0.003430000}, {11550, 0.003480000}, {11625,
    0.003520000}, {11700, 0.003560000}, {11775, 0.003600000}, {11850,
    0.003640000}, {11925, 0.003680000}, {12000, 0.003720000}, {12075,
    0.003750000}, {12150, 0.003790000}, {12225, 0.003830000}, {12300,
    0.003860000}, {12375, 0.003890000}, {12450, 0.003910000}, {12525,
    0.003930000}, {12600, 0.003950000}, {12675, 0.003970000}, {12750,
    0.003980000}, {12825, 0.003990000}, {12900, 0.004010000}, {12975,
    0.004010000}, {13050, 0.004020000}, {13125, 0.004030000}, {13200,
    0.004030000}, {13275, 0.004030000}, {13350, 0.004020000}, {13425,
    0.004020000}, {13500, 0.004000000}, {13575, 0.003990000}, {13650,
    0.003980000}, {13725, 0.003960000}, {13800, 0.003940000}, {13875,
    0.003920000}, {13950, 0.003900000}, {14025, 0.003870000}, {14100,
    0.003850000}, {14175, 0.003820000}, {14250, 0.003790000}, {14325,
    0.003760000}, {14400, 0.003730000}, {14475, 0.003700000}, {14550,
    0.003660000}, {14625, 0.003630000}, {14700, 0.003590000}, {14775,
    0.003550000}, {14850, 0.003500000}, {14925, 0.003460000}, {15000,
    0.003420000}, {15075, 0.003370000}, {15150, 0.003320000}, {15225,
    0.003270000}, {15300, 0.003220000}, {15375, 0.003170000}, {15450,
    0.003120000}, {15525, 0.003070000}, {15600, 0.003010000}, {15675,
    0.002960000}, {15750, 0.002910000}, {15825, 0.002850000}, {15900,
    0.002800000}, {15975, 0.002750000}, {16050, 0.002700000}, {16125,
    0.002650000}, {16200, 0.002600000}, {16275, 0.002550000}, {16350,
    0.002500000}, {16425, 0.002450000}, {16500, 0.002410000}, {16575,
    0.002360000}, {16650, 0.002320000}, {16725, 0.002280000}, {16800,
    0.002240000}, {16875, 0.002200000}, {16950, 0.002160000}, {17025,
    0.002130000}, {17100, 0.002100000}, {17175, 0.002060000}, {17250,
    0.002040000}, {17325, 0.002010000}, {17400, 0.001980000}, {17475,
    0.001950000}, {17550, 0.001930000}, {17625, 0.001900000}, {17700,
    0.001880000}, {17775, 0.001850000}, {17850, 0.001830000}, {17925,
    0.001800000}, {18000, 0.001780000}, {18075, 0.001760000}, {18150,
    0.001740000}, {18225, 0.001720000}, {18300, 0.001690000}, {18375,
    0.001680000}, {18450, 0.001660000}, {18525, 0.001640000}, {18600,
    0.001620000}, {18675, 0.001600000}, {18750, 0.001590000}, {18825,
    0.001570000}, {18900, 0.001550000}, {18975, 0.001540000}, {19050,
    0.001520000}, {19125, 0.001500000}, {19200, 0.001490000}, {19275,
    0.001480000}, {19350, 0.001460000}, {19425, 0.001450000}, {19500,
    0.001440000}, {19575, 0.001420000}, {19650, 0.001410000}, {19725,
    0.001400000}, {19800, 0.001390000}, {19875, 0.001380000}, {19950,
    0.001370000}, {20025, 0.001360000}, {20100, 0.001350000}, {20175,
    0.001350000}, {20250, 0.001340000}, {20325, 0.001330000}, {20400,
    0.001320000}, {20475, 0.001320000}, {20550, 0.001310000}, {20625,
    0.001300000}, {20700, 0.001300000}, {20775, 0.001290000}, {20850,
    0.001280000}, {20925, 0.001270000}, {21000, 0.001270000}, {21075,
    0.001260000}, {21150, 0.001250000}, {21225, 0.001250000}, {21300,
    0.001240000}, {21375, 0.001230000}, {21450, 0.001230000}, {21525,
    0.001220000}, {21600, 0.001210000}, {21675, 0.001210000}, {21750,
    0.001200000}, {21825, 0.001200000}, {21900, 0.001190000}, {21975,
    0.001190000}, {22050, 0.001180000}, {22125, 0.001170000}, {22200,
    0.001170000}, {22275, 0.001160000}, {22350, 0.001160000}, {22425,
    0.001150000}, {22500, 0.001150000}, {22575, 0.001140000}, {22650,
    0.001140000}, {22725, 0.001140000}, {22800, 0.001130000}, {22875,
    0.001130000}, {22950, 0.001120000}, {23025, 0.001120000}, {23100,
    0.001120000}, {23175, 0.001110000}, {23250, 0.001110000}, {23325,
    0.001110000}, {23400, 0.001100000}, {23475, 0.001100000}, {23550,
    0.001100000}, {23625, 0.001090000}, {23700, 0.001090000}, {23775,
    0.001090000}, {23850, 0.001080000}, {23925, 0.001080000}, {24000,
    0.001080000}, {24075, 0.001070000}, {24150, 0.001070000}, {24225,
    0.001070000}, {24300, 0.001060000}, {24375, 0.001060000}, {24450,
    0.001060000}, {24525, 0.001060000}, {24600, 0.001050000}, {24675,
    0.001050000}, {24750, 0.001050000}, {24825, 0.001050000}, {24900,
    0.001040000}, {24975, 0.001040000}, {25050, 0.001040000}, {25125,
    0.001040000}, {25200, 0.001040000}, {25275, 0.001030000}, {25350,
    0.001030000}, {25425, 0.001030000}, {25500, 0.001030000}, {25575,
    0.001020000}, {25650, 0.001020000}, {25725, 0.001020000}, {25800,
    0.001020000}, {25875, 0.001010000}, {25950, 0.001010000}, {26025,
    0.001010000}, {26100, 0.001010000}, {26175, 0.001010000}, {26250,
    0.001000000}, {26325, 0.001000000}, {26400, 0.001000000}, {26475,
    0.000998000}, {26550, 0.000997000}, {26625, 0.000995000}, {26700,
    0.000994000}, {26775, 0.000992000}, {26850, 0.000991000}, {26925,
    0.000989000}, {27000, 0.000987000}, {27075, 0.000986000}, {27150,
    0.000985000}, {27225, 0.000983000}, {27300, 0.000982000}, {27375,
    0.000980000}, {27450, 0.000979000}, {27525, 0.000977000}, {27600,
    0.000976000}, {27675, 0.000975000}, {27750, 0.000973000}, {27825,
    0.000972000}, {27900, 0.000970000}, {27975, 0.000969000}, {28050,
    0.000967000}, {28125, 0.000966000}, {28200, 0.000965000}, {28275,
    0.000963000}, {28350, 0.000962000}, {28425, 0.000961000}, {28500,
    0.000959000}, {28575, 0.000958000}, {28650, 0.000957000}, {28725,
    0.000956000}, {28800, 0.000954000}, {28875, 0.000953000}, {28950,
    0.000951000}, {29025, 0.000950000}, {29100, 0.000948000}, {29175,
    0.000946000}, {29250, 0.000945000}, {29325, 0.000943000}, {29400,
    0.000942000}, {29475, 0.000940000}, {29550, 0.000939000}, {29625,
    0.000937000}, {29700, 0.000935000}, {29775, 0.000934000}, {29850,
    0.000933000}, {29925, 0.000932000}, {30000, 0.000931000}};
model = ((q*k*t*\[Tau]^2)/(Pi*\[Omega]*\[Rho]))*(Im[
      2*\[Omega]*\[Tau]*I -
       Sqrt[1 + 2*\[Omega]*\[Tau]*I]]/(Abs[
        y + (1 + \[Omega]*\[Tau]*I)^2 -
         Sqrt[1 + 2*\[Omega]*\[Tau]*I]])^2);
fit = FindFit[
  data, {model, Im[\[Gamma]] == 0,
   Im[\[Eta]] == 0}, {\[Gamma], \[Eta]}, \[Omega]]
Show[ListPlot[data, PlotStyle -> {Red, PointSize[Large]}]]
modelf = Function[{\[Omega]}, Evaluate[model /. fit]]
Plot[modelf[\[Omega]], {\[Omega], 0, 30000},
Epilog -> Map[Point, data]]
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zsy312
发表于 2011-12-19 10:37:23 | 显示全部楼层 来自 河北张家口
模型合适吗?效果很差.
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