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[求助] matlab用fsolve解三元非線性方程出現(xiàn)問(wèn)題已有1人參與

首先定義了三個(gè)syms 變量 syms pH;  syms S_CO3H0; syms S_CaOH0;

通過(guò)一系列方程運(yùn)算最后得到netcharge，netCa，netCO3 三個(gè)變量，而這三個(gè)變量包含符號(hào)變量syms pH;  syms S_CO3H0; syms S_CaOH0;
利用inline函數(shù) 把符號(hào)變量轉(zhuǎn)化成函數(shù) 如下：
ionnumber=inline(netcharge)%將靜電荷的字符運(yùn)算轉(zhuǎn)化為函數(shù)
ioncalcium=inline(netCa)%將固體表面表面凈鈣數(shù)的字符運(yùn)算轉(zhuǎn)化為函數(shù)
ioncarbonate=inline(netCO3)%將固體表面表面凈碳酸根數(shù)的字符運(yùn)算轉(zhuǎn)化為函數(shù)

運(yùn)行顯示
Inline function:
   ionnumber(S_CO3H0,S_CaOH0,pH) = 2.*10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10))+10.^(-63./5+pH+log(10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10)))./log(10))+10.^(-16523792166633873./1407374883553280+pH+log(10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10)))./log(10))+10.^(-pH)-10.^(-6328041889942893./562949953421312+pH)-10.^(-14+pH)-2.*10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH)-7309029776373667./4611686018427387904.*S_CO3H0.*10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10))./(10.^(-pH))-3245861258160355./2048.*S_CaOH0.*10.^(-pH)+3715691980681023./295147905179352825856.*S_CO3H0./(10.^(-pH))+2096085705667255581572830407036923613418137./64903710731685345356631204115251200000000000000000.*S_CaOH0./(10.^(-pH))
Inline function:
   ioncalcium(S_CaOH0,pH) = 63904114710604247279./4611686018427387904.*S_CaOH0+3245861258160355./2048.*S_CaOH0.*10.^(-pH)+2096085705667255581572830407036923613418137./64903710731685345356631204115251200000000000000000.*S_CaOH0./(10.^(-pH))-4786177578236657./576460752303423488
Inline function:
   ioncarbonate(S_CO3H0,pH) = S_CO3H0+3715691980681023./295147905179352825856.*S_CO3H0./(10.^(-pH))+7309029776373667./4611686018427387904.*S_CO3H0.*10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10))./(10.^(-pH))-4786177578236657./576460752303423488
用fsolve 解上面那三個(gè)方程等于0的解如下
fsolve('ionnumber,ioncalcium,ioncarbonate',[8.3,0.002,0.002])

運(yùn)行結(jié)果：
??? Error using ==> fsolve
FSOLVE only accepts inputs of data type double.

Error in ==> carbonate at 48
fsolve('ionnumber','ioncalcium','ioncarbonate',[8.3,0.002,0.002])

求高手解答

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說(shuō)大話哄人慣了，連自己也哄相信-----這是極普通的心理現(xiàn)象

1樓 2015-01-05 17:00:39

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【答案】應(yīng)助回帖

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感謝參與，應(yīng)助指數(shù) +1
huawdong: 金幣+20, 非常感謝，在程序體中還有些變量可引起三個(gè)方程的形式發(fā)生變化，我想問(wèn)下在這種情況下怎么辦呢 2015-01-05 17:22:22

以下代碼完整復(fù)制進(jìn)一個(gè)m文件，運(yùn)行即可：

CODE:

function solve_noneqs

clear all;clc

format long

x0=[8.3,0.002,0.002];

options=optimset('TolFun',1e-9,'TolX',1e-9);

[x fval]=fsolve(@objfun,x0,options)

function f=objfun(x)

pH=x(1);

S_CaOH0=x(2);

S_CO3H0=x(3);

f(1)=2.*10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10))+10.^(-63./5+pH+log(10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10)))./log(10))+10.^(-16523792166633873./1407374883553280+pH+log(10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10)))./log(10))+10.^(-pH)-10.^(-6328041889942893./562949953421312+pH)-10.^(-14+pH)-2.*10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH)-7309029776373667./4611686018427387904.*S_CO3H0.*10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10))./(10.^(-pH))-3245861258160355./2048.*S_CaOH0.*10.^(-pH)+3715691980681023./295147905179352825856.*S_CO3H0./(10.^(-pH))+2096085705667255581572830407036923613418137./64903710731685345356631204115251200000000000000000.*S_CaOH0./(10.^(-pH));

f(2)=63904114710604247279./4611686018427387904.*S_CaOH0+3245861258160355./2048.*S_CaOH0.*10.^(-pH)+2096085705667255581572830407036923613418137./64903710731685345356631204115251200000000000000000.*S_CaOH0./(10.^(-pH))-4786177578236657./576460752303423488;

f(3)=S_CO3H0+3715691980681023./295147905179352825856.*S_CO3H0./(10.^(-pH))+7309029776373667./4611686018427387904.*S_CO3H0.*10.^(-212./25-log(10.^(-1033./100+log(10.^(-6328041889942893./562949953421312+pH))./log(10)+pH))./log(10))./(10.^(-pH))-4786177578236657./57646075230342348;

計(jì)算結(jié)果：
x =

7.523258389170919 0.000000174719325 0.000082481725874

三個(gè)方程的殘差fval =

1.0e-015 *

0.116631222290336 0.001734723475977 -0.180411241501588

贊一下

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MATLAB、MS小問(wèn)題、普通問(wèn)題請(qǐng)發(fā)帖求助！時(shí)間精力有限，恕不接受無(wú)償私信求助。

2樓2015-01-05 17:09:03

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在程序體中還有些變量可引起三個(gè)方程的形式發(fā)生變化時(shí)，把這些變量以基本自變量x定義出來(lái)即可。

贊一下

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3樓2015-01-05 18:44:27

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