MATLAB数学实验第二版答案胡良剑之欧阳文创编Word文件下载.docx
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删去绝对值最小的点以求函数绝对值次小的点
[f2,x2_index]=min(abs(f))求另一近似根函数绝对值次小的点
f2=
0.0630
x2_index=
65
x(x2_index)
1.2500
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eg2_1.m
function[xbar,s]=ex2_1(x)
n=length(x);
xbar=sum(x)/n;
s=sqrt((sum(x.^2)n*xbar^2)/(n1));
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=1e8;
a=(1+sqrt(5))/2;
whileabs(xa)>
e
k=k+1;
F(k)=F(k1)+F(k2);
x=F(k)/F(k1);
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:
0.1:
y=x.^2.*sin(x.^2x2);
plot(x,y)
y=inline('
x^2*sin(x^2x2)'
);
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.^22*x2*y2*x.^2.*y+6;
(5)
0.01:
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=1.5:
1.5;
y=1.1*(x>
1.1)+x.*(x<
=1.1).*(x>
=1.1)1.1*(x<
1.1);
page45,ex9
close;
a=0.5457;
b=0.7575;
p=a*exp(0.75*y.^23.75*x.^21.5*x).*(x+y>
1);
p=p+b*exp(y.^26*x.^2).*(x+y>
1).*(x+y<
=1);
p=p+a*exp(0.75*y.^23.75*x.^2+1.5*x).*(x+y<
mesh(x,y,p)
page45,ex10
lookforlyapunov
helplyap
A=[123;
456;
780];
C=[2522;
52456;
225616];
X=lyap(A,C)
X=
1.00001.00000.0000
1.00002.00001.0000
0.00001.00007.0000
Chapter3
Page65Ex1
a=[1,2,3];
b=[2,4,3];
a./b,a.\b,a/b,a\b
0.50000.50001.0000
221
0.6552一元方程组x[2,4,3]=[1,2,3]的近似解
000
0.66671.33331.0000
矩阵方程[1,2,3][x11,x12,x13;
x21,x22,x23;
x31,x32,x33]=[2,4,3]的特解
Page65Ex2
A=[411;
326;
153];
b=[9;
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=
2.3830
1.4894
2.0213
(2)
A=[433;
b=[1;
rank(A),rank([A,b])
0.4706
0.2941
0
A=[41;
32;
15];
1;
2
3可见方程组无解
0.3311
0.1219最小二乘近似解
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
0.6255
0.2085
0.4170
x0=
通解kx+x0
Page65Ex4
x0=[0.20.8]'
a=[0.990.05;
0.010.95];
x1=a*x,x2=a^2*x,x10=a^10*x
x=x0;
1000,x=a*x;
end,x
0.8333
0.1667
x0=[0.80.2]'
[v,e]=eig(a)
v=
0.98060.7071
0.19610.7071
e=
1.00000
00.9400
v(:
1)./x
1.1767
1.1767成比例,说明x是最大特征值对应的特征向量
Page65Ex5
用到公式(3.11)(3.12)
B=[6,2,1;
2.25,1,0.2;
3,0.2,1.8];
x=[25520]'
C=B/diag(x)
C=
0.24000.40000.0500
0.09000.20000.0100
0.12000.04000.0900
A=eye(3,3)C
A=
0.76000.40000.0500
0.09000.80000.0100
0.12000.04000.9100
D=[171717]'
x=A\D
37.5696
25.7862
24.7690
Page65Ex6
a=[411;
det(a),inv(a),[v,d]=eig(a)
94
0.25530.02130.0426
0.15960.13830.2234
0.18090.22340.0532
0.01850.90090.3066
0.76930.12400.7248
0.63860.41580.6170
d=
3.052700
03.67600
008.3766
a=[111;
021;
120];
2.00002.00001.0000
1.00001.00001.0000
2.00003.00002.0000
0.57730.5774+0.0000i0.57740.0000i
0.57730.57740.5774
0.57740.57730.0000i0.5773+0.0000i
1.000000
01.0000+0.0000i0
001.00000.0000i
A=[5765;
71087;
68109;
57910]
5765
71087
68109
57910
det(A),inv(A),[v,d]=eig(A)
68.000041.000017.000010.0000
41.000025.000010.00006.0000
17.000010.00005.00003.0000
10.00006.00003.00002.0000
0.83040.09330.39630.3803
0.50160.30170.61490.5286
0.20860.76030.27160.5520
0.12370.56760.62540.5209
0.0102000
00.843100
003.85810
00030.2887
(4)(以n=5为例)
方法一(三个for)
n=5;
n,a(i,i)=5;
(n1),a(i,i+1)=6;
(n1),a(i+1,i)=1;
a
方法二(一个for)
a=zeros(n,n);
a(1,1:
2)=[56];
fori=2:
(n1),a(i,[i1,i,i+1])=[156];
a(n,[n1n])=[15];
方法三(不用for)
a=diag(5*ones(n,1));
b=diag(6*ones(n1,1));
c=diag(ones(n1,1));
a=a+[zeros(n1,1),b;
zeros(1,n)]+[zeros(1,n);
c,zeros(n1,1)]
下列计算
det(a)
665
inv(a)
0.31730.58651.02861.62411.9489
0.09770.48870.85711.35341.6241
0.02860.14290.54290.85711.0286
0.00750.03760.14290.48870.5865
0.00150.00750.02860.09770.3173
[v,d]=eig(a)
0.78430.78430.92370.98600.9237
0.55460.55460.37710.00000.3771
0.26140.26140.00000.16430.0000
0.09240.09240.06280.00000.0628
0.02180.02180.02570.02740.0257
0.75740000
09.2426000
007.449500
0005.00000
00002.5505
Page65Ex7
[v,d]=eig(a)
det(v)
0.9255%v行列式正常,特征向量线性相关,可对角化
inv(v)*a*v验算
3.05270.00000.0000
0.00003.67600.0000
0.00000.00008.3766
[v2,d2]=jordan(a)也可用jordan
v2=
0.07980.00760.9127
0.18860.31410.1256
0.16050.26070.4213特征向量不同
d2=
8.376600
03.05270.0000i0
003.6760+0.0000i
v2\a*v2
8.376600.0000
0.00003.05270.0000
0.00000.00003.6760
1)./v2(:
2)对应相同特征值的特征向量成比例
2.4491
5.0566e0285.1918e017iv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
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
0.01020.00000.00000.0000
0.00000.84310.00000.0000
0.00000.00003.85810.0000
0.00000.0000030.2887
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=[4313;
2135;
1111;
3234;
7670]
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
0.50005.0000
0.50001.0000
05.0000
Page65Exercise10
a=[122;
224;
242]
0.33330.93390.1293
0.66670.33040.6681
0.66670.13650.7327
7.000000
02.00000
002.0000
v'
*v
1.00000.00000.0000
0.00001.00000
0.000001.0000v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
202i1=a;
53i2=c;
a3i3=c;
a4i4=b;
c5i5=b;
b3i6=0;
i1=i3+i4;
i5=i2+i3;
i6=i4+i5;
计算如下
A=[100200000;
001030000;
101003000;
110000400;
011000050;
010000003;
000101100;
000011010;
000000111];
b=[2050000000]'
A\b
13.3453
6.4401
8.5420
3.3274
1.1807
1.6011
1.7263
0.4204
2.1467
Page65Exercise12
left=sum(eig(A)),right=sum(trace(A))
left=
6.0000
right=
6
left=prod(eig(A)),right=det(A)原题有错,
(1)^n应删去
27.0000
27
fA=(Ap
(1)*eye(3,3))*(Ap
(2)*eye(3,3))*(Ap(3)*eye(3,3))
fA=
1.0e012*