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hnhyxhf

铜虫 (初入文坛)

[求助] mathematics软件解指数方程的命令

出(x1,y1), (x2,y2), (x3,y3)三组初值,请帮忙写一个mathematics程度求解 y=a*x^b+c 中三个参数 a,b,c的数值解?或者提供一个解指数方程的命令!
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zsy312

银虫 (小有名气)

【答案】应助回帖

★ ★ ★
小雨萌萌: 金币+3, 谢谢应助~ 2012-10-30 19:02:49
function = a*x^2 + b*x + c == y;
X = {1000, 650, 495};
Y = {10, 15, 20};
eqation = Table[eqn /. {x -> X[], y -> Y[]}, {i, 3}]
solution = Solve[eqn, {a, b, c}]


输出: {{a -> 39/1095850, b -> -(16001/219170), c -> 1039270/21917}}
注意[]在Mathematica中表示函数的定义, [[ ]]表示下标.
3楼2012-10-24 06:23:19
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hnhyxhf

铜虫 (初入文坛)

我写了一个简单的程序,但是,不知道为什么错了?请指点。

T = 3;
Array[y, T]; Array[x, Num];
Clear[a, b, c];
y[1] = 10; x[1] = 1000;
y[2] = 15; x[2] = 650;
y[3] = 20; x[3] = 495;
Roots[y[1] - a*x[1]^{b} - c ==
0 && y[2] - a*x[2]^{b} - c == 0 && y[3] - a*x[3]^{b} - c == 0, {a, b, c}]
2楼2012-10-20 10:02:44
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zsy312

银虫 (小有名气)

【答案】应助回帖

★
小雨萌萌: 金币+1, 3Q 2012-10-30 19:03:04
刚才忘记改了, 有一处变量改前没改后:
CODE:
function = a*x^2 + b*x + c == y;
X = {1000, 650, 495};
Y = {10, 15, 20};
eqation = Table[function /. {x -> X[], y -> Y[]}, {i, 3}]
solution = Solve[eqation, {a, b, c}]

4楼2012-10-24 06:49:27
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