5楼: Originally posted by 津津爱睡觉 at 2015-07-20 11:48:09
哇哇。。怎么都是负的啊。。说明我参数拟合错了。。我原方程是x=1/(x(2).*49.005^2).*..
xdata=
ydata=..我拟合出了方程中的参数x1,x2然后根据xdata求y值。。能不能再帮帮我啊。。感谢。。急求...

function solve_eqs
clear all;clc
format long

global x
y0=-0.1;
x_data=[0,0.25,0.5,0.75,1,1.25,1.5,1.75,2,2.25,2.5,3,3.5,4,4.5,5,5.5,6,6.5];
for i=1:length(x_data)
    x=x_data(i);
[y(i) fval(i)]=fsolve(@eqs,y0);
end

[x_data ;y; fval]'

function f=eqs(y)
global x
f=1/(15.3109*49.005^2).*(log((y./86.4241).*((86.4241-49.005)./(y-49.005)))-49.005.*(1./y-1./86.4241))-x;

LoopConstant x=[0,0.25,0.5,0.75,1,1.25,1.5,1.75,2,2.25,2.5,3,3.5,4,4.5,5,5.5,6,6.5];
Function
x=1/(15.3109*49.005^2)*(ln((y/86.4241)*((86.4241-49.005)/(y-49.005)))-49.005*(1/y-1/86.4241));

function solve_eqs
clear all;clc
format long

global x
y0=-0.1;
x_data=[0,0.25,0.5,0.75,1,1.25,1.5,1.75,2,2.25,2.5,3,3.5,4,4.5,5,5.5,6,6.5];
for i=1:length(x_data)
    x=x_data(i);
[y(i) fval(i)]=fsolve(@eqs,y0);
end

[x_data ;y; fval]'

2楼: Originally posted by dingd at 2015-07-20 10:55:11
用1stOpt很方便：

LoopConstant x=;
Function
x=1/(15.3109*49.005^2)*(ln((y/86.4241)*((86.4241-49.005)/(y-49.005)))-49.005*(1/y-1/86.4241));


x        y
0        -52.980531685766
0.25        -0.005325680664864
0 ...