中南大学材料学院MATLAB考试重点题目老师在最后几节课勾的题目汇总.docx
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中南大学材料学院MATLAB考试重点题目老师在最后几节课勾的题目汇总
P28
num0=1.785e-3;
>>a=0.03368;
>>b=0.000221;
>>t=0:
20:
80;
>>a=num0./(1+a*t+b*t.^2)
a=
0.00180.00100.00070.00050.0003
P88
[x,y]=meshgrid(-2:
0.2:
2,-2:
0.2:
2);
>>z=x.*exp(-x.^2-y.^2);
>>[px,py]=gradient(z,0.2,0.2);
>>contour(z);
>>holdon
>>quiver(px,py)
P101
>>x=1:
0.01*pi:
2*pi;
>>y=cos(x);
>>z=sin(x);
>>plot(x,y,'-.rd',x,z,'--k')
P104
>>x=1:
10;
>>y=rand(10,1);
>>bar(x,y);
>>x=0:
0.1*pi:
2*pi;
>>y=x.*sin(x);
>>feather(x,y)
P105
>>x=[2,4,6,8];
>>pie(x,{'math','english','chinese','music'});
P107
>>[x,y]=meshgrid(-2:
0.1:
2,-2:
0.1:
2);
>>z=x.*exp(-x.^2-y.^2);
>>plot3(x,y,z)
P109
x=-8:
0.5:
8;
y=x';
a=ones(size(y))*x;
b=y*ones(size(x));
c=sqrt(a.^2+b.^2)+eps;
z=sin(c)./c;
mesh(z)
P110
[X,Y]=meshgrid([-4:
0.5:
4]);%也可以是meshgrid(-4:
0.5:
4,-4:
0.5:
4)
Z=sqrt(X.^2+Y.^2);
meshc(X,Y,Z)
p113
x=0:
pi/20:
pi*3;
r=5+cos(x);
[a,b,c]=cylinder(r,30);
mesh(a,b,c)
P113
[a,b,c]=sphere(40);
t=abs(c);
surf(a,b,c,t);
axis('equal')
axis('square')
colormap('hot')
P118
x=1:
0.1*pi:
2*pi;
y=sin(x);
plot(x,y);
xlabel('x(0-2\pi)','FontWeight','bold')
ylabel('y=sin(x)','FontWeight','bold')
title('正弦函数')
P123
x=0:
0.01*pi:
2*pi;
y=cos(x);
z=sin(x);
plot(x,y,'-*')
holdon
plot(x,z,'-o')
plot(x,y+z,'-h')
legend('sin(x)','cos(x)','sin(x)+cos(x)',0)
holdoff%这里的holdoff主要是等下次调用时,以上的两个图形将不再保留
P124
x=0:
0.1*pi:
2*pi;
subplot(2,2,1);
plot(x,sin(x),'-*');
title('sin(x)');
subplot(2,2,2);
plot(x,cos(x),'-o');
title('cos(x)');
subplot(2,2,3);
title('sin(x).*cos(x)');plot(x,sin(x).*cos(x));%注意x是数组,故用sin(x)与其他表达式相乘的时候也要表达成sin(x).*cos(x)
subplot(2,2,4);
plot(x,sin(x)+cos(x),'-k');
title('sin(x)+cos(x)');
P222
x=0:
0.1:
10;
y=sin(x);
xi=0:
.25:
10;
yi=interp1(x,y,xi);%注意是插值法函数interp1
plot(x,y,'o',xi,yi)
P227
x=[0.5,1.0,1.5,2.0,2.5,3.0];
y=[1.75,2.45,3.81,4.80,8.00,8.60];
a=polyfit(x,y,2)
x1=[0.5:
0.05:
3.0];
y1=a(3)+a
(2)*x1+a
(1)*x1.^2;
plot(x,y,'*')
holdon
plot(x1,y1,'-r')
P228
x=[1925313844];
y=[19.032.349.073.398.8];
x1=x.^2
x1=[ones(5,1),x1']
ab=x1\y'
x0=[19:
0.2:
44];
y0=ab
(1)+ab
(2)*x0.^2;
clf%这里的clf是清除以前的图片
plot(x,y,'o')
holdon
plot(x0,y0,'-r')
P233
functiony=fun(t)
y=exp(-0.5*t).*sin(t+pi/6);%注意这边有点,当数组与数组相乘时,其中一个数组应表达成有.的形式
d=pi/1000;
>>t=0:
d:
3*pi;
>>nt=length(t);
>>y=fun(t);
>>sc=cumsum(y)*d;
>>scf=sc(nt)
scf=
0.9016
z=trapz(y)*d
z=
0.9008
P237
functionf=fun(x)
f=exp(-x/2);%编写函数时让系统自动形成m文件
quadl('fun',1,3,1e-10)
ans=
0.7668
P244
x=sym('x');
>>diff(sin(x^2))
ans=
2*cos(x^2)*x
P274
functionf=f(x,y)
f=[-21;998-999]*y+[2*sin(x);999*(cos(x)-sin(x))];
>>ode23('f',[010],[2,3]);
刚性比
>>a=[-21;998-999];
>>b1=max(abs(real(eig(a))));
>>b2=min(abs(real(eig(a))));
>>s=b1/b2
s=
1000
P275
>>dsolve('Df=f+sin(t)','f(pi/2)=0')
ans=
-1/2*cos(t)-1/2*sin(t)+1/2*exp(t)/(cosh(pi)+sinh(pi))^(1/2)
>>dsolve('D2y=-a^2*y','y(0)=1,Dy(pi/a)=0')
ans=
cos(a*t)
S=dsolve('Dx=y','Dy=-x','x(0)=0','y(0)=1')
S=
x:
[1x1sym]
y:
[1x1sym]
>>S.x
ans=
sin(t)
>>S.y
ans=
cos(t)
几点对dsolve的解释
dsolve('Dy=x+1','y(0)=0')
ans=
x*t+t%此时matlab软件自动将t看为默认变量,而将x看成一个常数
P246
a=[0.40960.12340.36780.2943
0.22460.38720.40150.1129
0.36450.19200.37810.0643
0.17840.40020.27860.3927];
>>b=[0.4043
0.1550
0.4240
-0.2557];
>>a\b
ans=
-0.1819
-1.6630
2.2172
-0.4467
P265
functiony=fc(x)
y
(1)=x
(1)-0.7*sin(x
(1))-0.2*cos(x
(2));
y
(2)=x
(2)-0.7*cos(x
(1))+0.2*sin(x
(2));
x0=[0.50.5];
>>fsolve('fc',x0)%这里的x0为初始值
ans=
0.52650.5079
比较fzero函数
例如求x^2+x-1=0的解
fzero('x^2+x-1',0.5)%这里的0.5是初始值,初始值只是影响运行时间,对算出的结果影响不大
ans=
0.6180
P307
x=[0.2360.2380.2480.2450.243
0.2570.2530.2550.2540.261
0.2580.2640.2590.2670.262];
anova1(x')%anova1是一个对单因素试验的方差分析,它返回的是原假设均值相等的几率值
ans=
1.3431e-005
P308
x=[58.200056.200065.3000
52.600041.200060.8000
49.100054.100051.6000
42.800050.500048.4000
60.100070.900039.2000
58.300073.200040.7000
75.800058.200048.7000
71.500051.000041.4000];
anova2(x,2)
ans=
0.00350.02600.0001
P309
x=[100:
10:
190];
>>y=[45515461667074788589];
>>[a,b]=polyfit(x,y,1)
a=
0.4830-2.7394
b=
R:
[2x2double]
df:
8
normr:
2.6878
>>plot(x,y,'*')
>>holdon
>>y=a
(1)*x+a
(2);
>>plot(x,y)
P265
Fsolve的功能
functiony=fc(x)
y
(1)=x
(1)-0.7*sin(x
(1))-0.2*cos(x
(2));
y
(2)=x
(2)-0.7*cos(x
(1))+0.2*sin(x
(2));
y=[y
(1)y
(2)];
x0=[0.50.5];
>>fsolve('fc',x0)
ans=
0.52650.5079
P310
>>x=normrnd(0,1,100000,1);
>>normplot(x)
练习题
1.求函数在指定点的数值导数
x=sym('x');
>>y=[xx.^2x.^3;12*x3*x.^2;026*x];
>>x=1;
>>eval(diff(y))
ans=
123
026
006
>>x=2;
>>eval(diff(y))
ans=
1412
0212
006
>>x=3;
>>eval(diff(y))
ans=
1627
0218
006
2.求下列函数导数
(1)
x=sym('x');
>>y=x^10+10^x+(log(10))/log(x);
>>diff(y)
ans=
10*x^9+10^x*log(10)-2592480341699211/1125899906842624/log(x)^2/x
(2)
x=sym('x');
>>y=log(1+x);
>>x=1;
>>eval(diff(y,2))%在x=1的条件下对y表达式求两次导数后导函数的值
ans=
-0.2500
3.用数值方法求下列积分
首先先讲一下trapz的用法,如下题
t=0:
0.001:
1;
>>y=t;
>>trapz(t,y)
ans=
0.5000
(1)
>>x=1:
0.01:
5;
>>y=(x.^2).*sqrt(2*x.^2+3);
>>trapz(x,y)
ans=
232.8066
(2)
x=pi/4:
0.01:
pi/3;
>>y=x./(sin(x).^2);
>>trapz(x,y)
ans=
0.3810
第三题拟合曲线题
x=[0:
0.1:
1];
>>y=[-0.4471.9783.286.167.087.347.669.569.489.3011.2];
>>a=polyfit(x,y,2);
>>x=[0.05:
0.2:
1.05];
>>y=a(3)+a
(2)*x+a
(1)*x.^2%注意x要在y前先赋值,不然y不会运行为最新的x对呀的y值y=0.95034.38757.03988.90739.989910.2876