MATLAB数学实验第二版答案胡良剑文档格式.docx
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x2_index=
65
x(x2_index)
Page20,ex5
z=magic(10)
z=
929918156774515840
9880714167355576441
4818820225456637047
8587192136062697128
869325296168755234
17247683904249263365
2358289914830323966
7961395972931384572
10129496783537444653
111810077843643502759
sum(z)
sum(diag(z))
z(:
2)/sqrt(3)
z(8,:
)=z(8,:
)+z(3,:
)
Chapter2
Page45ex1
先在编辑器窗口写下列M函数,保存为
function[xbar,s]=ex2_1(x)
n=length(x);
xbar=sum(x)/n;
s=sqrt((sum(x.^2)-n*xbar^2)/(n-1));
例如
x=[81706551766690876177];
[xbar,s]=ex2_1(x)
Page45ex2
s=log
(1);
n=0;
whiles<
=100
n=n+1;
s=s+log(1+n);
end
m=n
Page40ex3
clear;
F
(1)=1;
F
(2)=1;
k=2;
x=0;
e=1e-8;
a=(1+sqrt(5))/2;
whileabs(x-a)>
e
k=k+1;
F(k)=F(k-1)+F(k-2);
x=F(k)/F(k-1);
a,x,k
计算至k=21可满足精度
Page45ex4
tic;
s=0;
fori=1:
1000000
s=s+sqrt(3)/2^i;
s,toc
i=1;
whilei<
=1000000
i=i+1;
i=1:
1000000;
s=sqrt(3)*sum(1./2.^i);
Page45ex5
t=0:
24;
c=[15141414141516182022232528...
313231292725242220181716];
plot(t,c)
Page45ex6
(1)
x=-2:
y=x.^2.*sin(x.^2-x-2);
plot(x,y)
y=inline('
x^2*sin(x^2-x-2)'
);
fplot(y,[-22])
(2)参数方法
t=linspace(0,2*pi,100);
x=2*cos(t);
y=3*sin(t);
plot(x,y)
(3)
x=-3:
3;
y=x;
[x,y]=meshgrid(x,y);
z=x.^2+y.^2;
surf(x,y,z)
(4)
y=-3:
13;
z=x.^4+3*x.^2+y.^2-2*x-2*y-2*x.^2.*y+6;
(5)
2*pi;
x=sin(t);
y=cos(t);
z=cos(2*t);
plot3(x,y,z)
(6)
theta=linspace(0,2*pi,50);
fai=linspace(0,pi/2,20);
[theta,fai]=meshgrid(theta,fai);
x=2*sin(fai).*cos(theta);
y=2*sin(fai).*sin(theta);
z=2*cos(fai);
(7)
x=linspace(0,pi,100);
y1=sin(x);
y2=sin(x).*sin(10*x);
y3=-sin(x);
plot(x,y1,x,y2,x,y3)
page45,ex7
x=:
;
y=*(x>
+x.*(x<
=.*(x>
=*(x<
page45,ex9
close;
a=;
b=;
p=a*exp*y.^*x.^*x).*(x+y>
1);
p=p+b*exp(-y.^2-6*x.^2).*(x+y>
-1).*(x+y<
=1);
p=p+a*exp*y.^*x.^2+*x).*(x+y<
=-1);
mesh(x,y,p)
page45,ex10
lookforlyapunov
helplyap
A=[123;
456;
780];
C=[2-5-22;
-5-24-56;
-22-56-16];
X=lyap(A,C)
X=
Chapter3
Page65Ex1
a=[1,2,3];
b=[2,4,3];
a./b,a.\b,a/b,a\b
221
一元方程组x[2,4,3]=[1,2,3]的近似解
000
矩阵方程[1,2,3][x11,x12,x13;
x21,x22,x23;
x31,x32,x33]=[2,4,3]的特解
Page65Ex2
A=[41-1;
32-6;
1-53];
b=[9;
-2;
1];
rank(A),rank([A,b])[A,b]为增广矩阵
3
3可见方程组唯一解
x=A\b
x=
(2)
A=[4-33;
b=[-1;
rank(A),rank([A,b])
0
(3)
A=[41;
32;
1-5];
b=[1;
1;
2
3可见方程组无解
最小二乘近似解
(4)
a=[2,1,-1,1;
1,2,1,-1;
1,1,2,1];
b=[123]'
%注意b的写法
rank(a),rank([a,b])
3rank(a)==rank([a,b])<
4说明有无穷多解
a\b
1
0一个特解
Page65Ex3
b=[1,2,3]'
x=null(a),x0=a\b
x0=
通解kx+x0
Page65Ex4
x0=[]'
a=[;
];
x1=a*x,x2=a^2*x,x10=a^10*x
x=x0;
1000,x=a*x;
end,x
[v,e]=eig(a)
v=
e=
0
v(:
1)./x
成比例,说明x是最大特征值对应的特征向量
Page65Ex5
用到公式
B=[6,2,1;
1,;
3,,];
x=[25520]'
C=B/diag(x)
C=
A=eye(3,3)-C
A=
D=[171717]'
x=A\D
Page65Ex6
a=[41-1;
det(a),inv(a),[v,d]=eig(a)
-94
d=
00
00
a=[11-1;
02-1;
-120];
+-
-+
0+0
00-
A=[5765;
71087;
68109;
57910]
5765
71087
68109
57910
det(A),inv(A),[v,d]=eig(A)
000
(4)(以n=5为例)
方法一(三个for)
n=5;
n,a(i,i)=5;
(n-1),a(i,i+1)=6;
(n-1),a(i+1,i)=1;
a
方法二(一个for)
a=zeros(n,n);
a(1,1:
2)=[56];
fori=2:
(n-1),a(i,[i-1,i,i+1])=[156];
a(n,[n-1n])=[15];
方法三(不用for)
a=diag(5*ones(n,1));
b=diag(6*ones(n-1,1));
c=diag(ones(n-1,1));
a=a+[zeros(n-1,1),b;
zeros(1,n)]+[zeros(1,n);
c,zeros(n-1,1)]
下列计算
det(a)
665
inv(a)
[v,d]=eig(a)
0000
0000
Page65Ex7
[v,d]=eig(a)
det(v)
%v行列式正常,特征向量线性相关,可对角化
inv(v)*a*v验算
[v2,d2]=jordan(a)也可用jordan
v2=
特征向量不同
d2=
0-0
00+
v2\a*v2
1)./v2(:
2)对应相同特征值的特征向量成比例
(2)
v的行列式接近0,特征向量线性相关,不可对角化
[v,d]=jordan(a)
101
100
1-10
110
011
001jordan标准形不是对角的,所以不可对角化
[v,d]=eig(A)
inv(v)*A*v
本题用jordan不行,原因未知
(4)
参考6(4)和7
(1)
Page65Exercise8
只有(3)对称,且特征值全部大于零,所以是正定矩阵.
Page65Exercise9
a=[4-313;
2-135;
1-1-1-1;
3-234;
7-6-70]
rank(a)
rank(a(1:
3,:
))
rank(a([124],:
))1,2,4行为最大无关组
b=a([124],:
)'
c=a([35],:
b\c线性表示的系数
Page65Exercise10
a=[1-22;
-2-24;
24-2]
v'
*v
0v确实是正交矩阵
Page65Exercise11
设经过6个电阻的电流分别为i1,...,i6.列方程组如下
20-2i1=a;
5-3i2=c;
a-3i3=c;
a-4i4=b;
c-5i5=b;
b-3i6=0;
i1=i3+i4;
i5=i2+i3;
i6=i4+i5;
计算如下
A=[100200000;
001030000;
10-100-3000;
1-10000-400;
0-110000-50;
01000000-3;
00010-1-100;
0000-1-1010;
000000-1-11];
b=[2050000000]'
A\b
Page65Exercise12
left=sum(eig(A)),right=sum(trace(A))
left=
right=
6
left=prod(eig(A)),right=det(A)原题有错,(-1)^n应删去
27
fA=(A-p
(1)*eye(3,3))*(A-p
(2)*eye(3,3))*(A-p(3)*eye(3,3))
fA=
*
norm(fA)f(A)范数接近0
Chapter4
Page84Exercise1
roots([111])
roots([30-402-1])
p=zeros(1,24);
p([1171822])=[5-68-5];
roots(p)
p1=[23];
p2=conv(p1,p1);
p3=conv(p1,p2);
p3(end)=p3(end)-4;
%原p3最后一个分量-4
roots(p3)
Page84Exercise2
fun=inline('
x*log(sqrt(x^2-1)+x)-sqrt(x^2-1)*x'
fzero(fun,2)
Page84Exercise3
x^4-2^x'
fplot(fun,[-22]);
gridon;
fzero(fun,-1),fzero(fun,1),fminbnd(fun,,
Page84Exercise4
x*sin(1/x)'
'
x'
fplot(fun,[]);
x=zeros(1,10);
10,x(i)=fzero(fun,*;
end;
x=[x,-x]
Page84Exercise5
[9*x
(1)^2+36*x
(2)^2+4*x(3)^2-36;
x
(1)^2-2*x
(2)^2-20*x(3);
16*x
(1)-x
(1)^3-2*x
(2)^2-16*x(3)^2]'
[a,b,c]=fsolve(fun,[000])
Page84Exercise6
fun=@(x)[x
(1)*sin(x
(1))*cos(x
(2)),x
(2)*cos(x
(1))+*sin(x
(2))];
[a,b,c]=fsolve(fun,[])
Page84Exercise7
close;
t=0:
pi/100:
x1=2+sqrt(5)*cos(t);
y1=3-2*x1+sqrt(5)*sin(t);
x2=3+sqrt
(2)*cos(t);
y2=6*sin(t);
plot(x1,y1,x2,y2);
gridon;
作图发现4个解的大致位置,然后分别求解
y1=fsolve('
[(x
(1)-2)^2+(x
(2)-3+2*x
(1))^2-5,2*(x
(1)-3)^2+(x
(2)/3)^2-4]'
[,2])
y2=fsolve('
[,-2])
y3=fsolve('
[,-5])
y4=fsolve('
[4,-4])
Page84Exercise8
x.^2.*sin(x.^2-x-2)'
作图观察
x
(1)=-2;
x(3)=fminbnd(fun,-1,;
x(5)=fminbnd(fun,1,2);
fun2=inline('
-x.^2.*sin(x.^2-x-2)'
x
(2)=fminbnd(fun2,-2,-1);
x(4)=fminbnd(fun2,,;
x(6)=2
feval(fun,x)
答案:
以上x
(1)(3)(5)是局部极小,x
(2)(4)(6)是局部极大,从最后一句知道x
(1)全局最小,x
(2)最大。
3*x.^5-20*x.^3+10'
fplot(fun,[-33]);
x
(1)=-3;
x(3)=fminsearch(fun,;
-(3*x.^5-20*x.^3+10)'
x
(2)=fminsearch(fun2,;
x(4)=3;
abs(x^3-x^2-x-2)'
fplot(fun,[03]);
fminbnd(fun,,
-abs(x^3-x^2-x-2)'
fminbnd(fun2,,
Page84Exercise9
y=-7:
z=y.^3/9+3*x.^2.*y+9*x.^2+y.^2+x.*y+9;
mesh(x,y,z);
x
(2)^3/9+3*x
(1)^2*