用matlab解方程

1. 用matlab解方程

参考代码：
>> syms w kc real>> Tjw = 7.8*kc/(7.8*kc-0.11*w^2+j*w);>> solve(abs(Tjw)-sqrt(sym(1)/2),w) ans =   2/11*(-1250+2145*kc+5*(-214500*kc+62500+368082*abs(kc)^2)^(1/2))^(1/2) -2/11*(-1250+2145*kc+5*(-214500*kc+62500+368082*abs(kc)^2)^(1/2))^(1/2)  2/11*(-1250+2145*kc-5*(-214500*kc+62500+368082*abs(kc)^2)^(1/2))^(1/2) -2/11*(-1250+2145*kc-5*(-214500*kc+62500+368082*abs(kc)^2)^(1/2))^(1/2)求出的四个根中，在kc>0的条件下，后两个为复数，第二个为负数，所以有效解其实只有第一个。

2. 用matlab解方程

【1】可以用dsolve（）函数求得，其解析值。然后再用plot（）函数绘制t～x(t)，t～y(t)的图像。实现代码
syms x(t) y(t)
Dx=diff(x,1);Dy=diff(y,1);
[x,y]=dsolve(Dx==2*x+3*y,Dy==2*x+y,x(0)==-2.7,y(0)==2.8);
t=0:0.1:10;x=eval(x);y=eval(y);
plot(t,x,t,y),hold on
xlabel('t'),ylabel('x(t),y(t)')
【2】可以用ode45（）函数求得，其数值值。然后再用plot（）函数绘制t～x(t)，t～y(t)，t～z(t)的图像。实现代码
x0=[0 1 1];
[t,x]=ode45(@func,[0 12],x0); 
disp([t x])
plot(t,x),grid on
xlabel('t'),ylabel('x(t),y(t),z(t)')
运行结果

3. 用matlab解方程

syms x
solve('(0.2-x)(0.06-2*x)^2==1.17*10^-5',x)

4. 用matlab求解方程

>> syms w c p r
>> s=solve('w/(2*3.14)-c/(2*l)*(15.68-w*p^2/(w^2+i*r*w))')
 s =
                                                                                                                                                                                                                                                         1.0*r*i
 -(3.14*10^(-33)*(- 7.84*10^33*c + 159235668789808917197452229299366.0*l*r*i + 7.84*10^33*(c^2 - 0.0051812938876317457959395899267025*c*l*p^2 + 0.040621344079032887040166385025348*c*l*r*i - 0.00041252339869679504744741958015147*l^2*r^2)^(1/2)))/l
    (3.14*10^(-33)*(7.84*10^33*c - 159235668789808917197452229299366.0*l*r*i + 7.84*10^33*(c^2 - 0.0051812938876317457959395899267025*c*l*p^2 + 0.040621344079032887040166385025348*c*l*r*i - 0.00041252339869679504744741958015147*l^2*r^2)^(1/2)))/l

5. matlab里面怎么解方程？

（1）y=sinx
已知y的值
怎么求x
,很简单：
x=asin(y),即是求解y。
（2）
方程组怎么解
比如
2*sin(x)+sin(y)=1和x+y=1求出x,y的值
程序如下：
a=solve('2*sin(x)+sin(y)=1','x+y=1');
x=eval(a.x);
y=eval(a.y);
求得x=0.1125,y=0.8875
或者
x=1.9832,y=-0.9832
注意三角函数中默认的是弧度

6. matlab解方程

clear all
close all
a=1.06615402141683*exp(-5);
b=0.00898235839599425;
c=1535.16643950786;
y=[-40:10:150]';
ly=length(y);
for k=1:1:ly;
    x1(k)=(-b+sqrt(b^2-4*a*(c-y(k))))/(2*a);
    x2(k)=(-b-sqrt(b^2-4*a*(c-y(k))))/(2*a);
end
x=[x1' x2'];
x=[-0.625191182025220 - 468.262164273482i -0.625191182025220 + 468.262164273482i
-0.625191182025220 - 466.773405520361i -0.625191182025220 + 466.773405520361i
-0.625191182025220 - 465.279883201568i -0.625191182025220 + 465.279883201568i
-0.625191182025220 - 463.781551296572i -0.625191182025220 + 463.781551296572i
-0.625191182025220 - 462.278363039030i -0.625191182025220 + 462.278363039030i
-0.625191182025220 - 460.770270899756i -0.625191182025220 + 460.770270899756i
-0.625191182025220 - 459.257226569190i -0.625191182025220 + 459.257226569190i
-0.625191182025220 - 457.739180939337i -0.625191182025220 + 457.739180939337i
-0.625191182025220 - 456.216084085167i -0.625191182025220 + 456.216084085167i
-0.625191182025220 - 454.687885245467i -0.625191182025220 + 454.687885245467i
-0.625191182025220 - 453.154532803087i -0.625191182025220 + 453.154532803087i
-0.625191182025220 - 451.615974264612i -0.625191182025220 + 451.615974264612i
-0.625191182025220 - 450.072156239379i -0.625191182025220 + 450.072156239379i
-0.625191182025220 - 448.523024417871i -0.625191182025220 + 448.523024417871i
-0.625191182025220 - 446.968523549415i -0.625191182025220 + 446.968523549415i
-0.625191182025220 - 445.408597419195i -0.625191182025220 + 445.408597419195i
-0.625191182025220 - 443.843188824526i -0.625191182025220 + 443.843188824526i
-0.625191182025220 - 442.272239550386i -0.625191182025220 + 442.272239550386i
-0.625191182025220 - 440.695690344147i -0.625191182025220 + 440.695690344147i
-0.625191182025220 - 439.113480889501i -0.625191182025220 + 439.113480889501i
];

7. Matlab 解方程

此方程组无解，对增广矩阵进行高斯消去，得到始终无解的方程（最后一行，画蓝线）

8. matlab 解方程

m=[];
p=[];
F=@(y,x)-y(1)*y(2)-y(2)+sin(y(1))-y(1)*x;
y=lsqcurvefit(F,[1 1],m,p)
%y即为所拟合函数系数,分别为x,y的值。