Matlab习题练习1(4)

2019-08-30 21:43

A =

1 2 3 -5 2 0 min = -5

37.使用MATLAB语言进行编程：打印出所有的水仙花数。所谓“水仙花数”，是指一个三位数，其各位数字立方之和等于该数本身。 for k = 100:999 a = fix(k/100); b = rem(fix(k/10),10); c = rem(k,10); if a.^3 + b.^3 + c.^3 == k fprintf( “%u,\\t\\t”, k ) ; end end

38.（15分）编写程序：计算 1+2+…+n<2000 时的最大 n 值；（编写函数文件：用 for 循环结构） function sum_for sum=0; for i=1:500

sum=sum+i; if sum>=2000 break; end end i=i-1

39. 试求出如下极限。(提示：用函数)

（1）lim(3?9)；（2）limx??xx1xxyxy?1?1x?0y?0；（3）limx?0y?01?cos(x2?y2)(x?y)e22x2?y2

（1）>> syms x;f=(3^x+9^x)^(1/x);

l=limit(f,x,inf)

l = 9

（2）>> syms x y;f=x*y/(sqrt(x*y+1)-1);limit(limit(f,x,0),y,0) ans =

（3）>> syms x y;f=(1-cos(x^2+y^2))*exp(x^2+y^2)/(x^2+y^2);limit(limit(f,x,0),y,0)

ans =0

?x?lncostdyd2y40. 已知参数方程?，试求出和2dxy?cost?tsintdx?

>> syms t;x=log(cos(t));y=cos(t)-t*sin(t);diff(y,t)/diff(x,t) ans =

-(-2*sin(t)-t*cos(t))/sin(t)*cos(t)

>> f=diff(y,t,2)/diff(x,t,2);subs(f,t,sym(pi)/3) ans =

3/8-1/24*pi*3^(1/2)

41. 假设f(x,y)?t??/3(提示：用函数)

?xy0x?2f?2f?2fedt，试求?2?2 2y?x?x?y?y?t2

>> syms x y t

>> s=int(exp(-t^2),t,0,x*y);

>> x/y*diff(f,x,2)-2*diff(diff(f,x),y)+diff(f,y,2) ans =

2*x^2*y^2*exp(-x^2*y^2)-2*exp(-x^2*y^2)-2*x^3*y*exp(-x^2*y^2)

42. 试求出下面的极限。(提示：用函数)

（1）lim?（2）limn(n???1?111??????； 222n??22?14?16?1(2n)?1??1111?????)

n2??n2?2?n2?3?n2?n?

（1）

>> syms k n;symsum(1/((2*k)^2-1),k,1,inf)

ans = 1/2

>> limit(symsum(1/((2*k)^2-1),k,1,n),n,inf)

ans = 1/2 （2）

>> limit(n*symsum(1/(n^2+k*pi),k,1,n),n,inf) ans = 1

43. 试求出以下的曲线积分。(提示：用函数)

（1）(x?y)ds，l为曲线x?a(cost?tsint)，y?a(sint?tcost)，

l?22

(0?t?2?)。

22222 （2）(yx?e)dx?(xy?xe?2y)dy，其中l为ax?by?c正向上半椭圆。

?3y3yl

（1） >> syms a t;x=a*(cos(t)+t*sin(t));y=a*(sin(t)-t*cos(t));

>> f=x^2+y^2;I=int(f*sqrt(diff(x,t)^2+diff(y,t)^2),t,0,2*pi)

I =

2*a^2*pi^2*(a^2)^(1/2)+4*a^2*pi^4*(a^2)^(1/2) （2）

>> syms x y a b c t;x=c*cos(t)/a;y=c*sin(t)/b; >> P=y*x^3+exp(y);Q=x*y^3+x*exp(y)-2*y; >> ds=[diff(x,t);diff(y,t)];I=int([P Q]*ds,t,0,pi) I =

-2/15*c*(-2*c^4+15*b^4)/b^4/a

?a4?4?b44. 试求出Vandermonde矩阵A??c4?4?d?e4?a3b3c3d3e3a2b2c2d2e2a1??b1?c1?的行列式，并以最简的形式显示结

?d1?e1??果。(提示：用函数)

>> syms a b c d e;A=vander([a b c d e]) A =

[ a^4, a^3, a^2, a, 1] [ b^4, b^3, b^2, b, 1] [ c^4, c^3, c^2, c, 1] [ d^4, d^3, d^2, d, 1] [ e^4, e^3, e^2, e, 1]

>> det(A), simple(ans) ans =

a^4*b^3*c^2*d-a^4*b^3*c^2*e-a^4*b^3*d^2*c+a^4*b^3*d^2*e+a^4*b^3*e^2*c-a^4*b^3*e^2*d-a^4*c^3*b^2*d+a^4*c^3*b^2*e+a^4*c^3*d^2*b-a^4*c^3*d^2*e-a^4*c^3*e^2*b+a^4*c^3*e^2*d+a^4*d^3*b^2*c-a^4*d^3*b^2*e-a^4*d^3*c^2*b+a^4*d^3*c^2*e+a^4*d^3*e^2*b-a^4*d^3*e^2*c-a^4*e^3*b^2*c+a^4*e^3*b^2*d+a^4*e^3*c^2*b-a^4*e^3*c^2*d-a^4*e^3*d^2*b+a^4*e^3*d^2*c-b^4*a^3*c^2*d+b^4*a^3*c^2*e+b^4*a^3*d^2*c-b^4*a^3*d^2*e-b^4*a^3*e^2*c+b^4*a^3*e^2*d+b^4*c^3*a^2*d-b^4*c^3*a^2*e-b^4*c^3*d^2*a+b^4*c^3*d^2*e+b^4*c^3*e^2*a-b^4*c^3*e^2*d-b^4*d^3*a^2*c+b^4*d^3*a^2*e+b^4*d^3*c^2*a-b^4*d^3*c^2*e-b^4*d^3*e^2*a+b^4*d^3*e^2*c+b^4*e^3*a^2*c-b^4*e^3*a^2*d-b^4*e^3*c^2*a+b^4*e^3*c^2*d+b^4*e^3*d^2*a-b^4*e^3*d^2*c+c^4*a^3*b^2*d-c^4*a^3*b^2*e-c^4*a^3*d^2*b+c^4*a^3*d^2*e+c^4*a^3*e^2*b-c^4*a^3*e^2*d-c^4*b^3*a^2*d+c^4*b^3*a^2*e+c^4*b^3*d^2*a-c^4*b^3*d^2*e-c^4*b^3*e^2*a+c^4*b^3*e^2*d+c^4*d^3*a^2*b-c^4*d^3*a^2*e-c^4*d^3*b^2*a+c^4*d^3*b^2*e+c^4*d^3*e^2*a-c^4*d^3*e^2*b-c^4*e^3*a^2*b+c^4*e^3*a^2*d+c^4*e^3*b^2*a-c^4*e^3*b^2*d-c^4*e^3*d^2*a+c^4*e^3*d^2*b-d^4*a^3*b^2*c+d^4*a^3*b^2*e+d^4*a^3*c^2*b-d^4*a^3*c^2*e-d^4*a^3*e^2*b+d^4*a^3*e^2*c+d^4*b^3*a^2*c-d^4*b^3*a^2*e-d^4*b^3*c^2*a+d^4*b^3*c^2*e+d^4*b^3*e^2*a-d^4*b^3*e^2*c-d^4*c^3*a^2*b+d^4*c^3*a^2*e+d^4*c^3*b^2*a-d^4*c^3*b^2*e-d^4*c^3*e^2*a+d^4*c^3*e^2*b+d^4*e^3*a^2*b-d^4*e^3*a^2*c-d^4*e^3*b^2*a+d^4*e^3*b^2*c+d^4*e^3*c^2*a-d^4*e^3*c^2*b+e^4*a^3*b^2*c-e^4*a^3*b^2*d-e^4*a^3*c^2*b+e^4*a^3*c^2*d+e^4*a^3*d^2*b-e^4*a^3*d^2*c-e^4*b^3*a^2*c+e^4*b^3*a^2*d+e^4*b^3*c^2*a-e^4*b^3*c^2*d-e^4*b^3*d^2*a+e^4*b^3*d^2*c+e^4*c^3*a^2*b-e^4*c^3*a^2*d-e^4*c^3*b^2*a+e^4*c^3*b^2*d+e^4*c^3*d^2*a-e^4*c^3*d^2*b-e^4*d^3*a^2*b+e^4*d^3*a^2*c+e^4*d^3*b^2*a-e^4*d^3*b^2*c-e^4*d^3*c^2*a+e^4*d^3*c^2*b

simplify:

*e^3*b^2*d+a^4*e^3*c^2*b-a^4*e^3*c^2*d-a^4*e^3*d^2*b+a^4*e^3*d^2*c-b^4*a^3*c^2*d+b^4*a^3*c^2*e+b^4*a^3*d^2*c-b^4*a^3*d^2*e-b^4*a^3*e^2*c+b^4*a^3*e^2*d+b^4*c^3*a^2*d-b^4*c^3*a^2*e-b^4*c^3*d^2*a+b^4*c^3*d^2*e+b^4*c^3*e^2*a-b^4*c^3*e^2*d-b^4*d^3*a^2*c+b^4*d^3*a^2*e+b^4*d^3*c^2*a-b^4*d^3*c^2*e-b^4*d^3*e^2*a+b^4*d^3*e^2*c+b^4*e^3*a^2*c-b^4*e^3*a^2*d-b^4*e^3*c^2*a+b^4*e^3*c^2*d+b^4*e^3*d^2*a-b^4*e^3*d^2*c+c^4*a^3*b^2*d-c^4*a^3*b^2*e-c^4*a^3*d^2*b+c^4*a^3*d^2*e+c^4*a^3*e^2*b-c^4*a^3*e^2*d-c^4*b^3*a^2*d+c^4*b^3*a^2*e+c^4*b^3*d^2*a-c^4*b^3*d^2*e-c^4*b^3*e^2*a+c^4*b^3*e^2*d+c^4*d^3*a^2*b-c^4*d^3*a^2*e-c^4*d^3*b^2*a+c^4*d^3*b^2*e+c^4*d^3*e^2*a-c^4*d^3*e^2*b-c^4*e^3*a^2*b+c^4*e^3*a^2*d+c^4*e^3*b^2*a-c^4*e^3*b^2*d-c^4*e^3*d^2*a+c^4*e^3*d^2*b-d^4*a^3*b^2*c+d^4*a^3*b^2*e+d^4*a^3*c^2*b-d^4*a^3*c^2*e-d^4*a^3*e^2*b+d^4*a^3*e^2*c+d^4*b^3*a^2*c-d^4*b^3*a^2*e-d^4*b^3*c^2*a+d^4*b^3*c^2*e+d^4*b^3*e^2*a-d^4*b^3*e^2*c-d^4*c^3*a^2*b+d^4*c^3*a^2*e+d^4*c^3*b^2*a-d^4*c^3*b^2*e-d^4*c^3*e^2*a+d^4*c^3*e^2*b+d^4*e^3*a^2*b-d^4*e^3*a^2*c-d^4*e^3*b^2*a+d^4*e^3*b^2*c+d^4*e^3*c^2*a-d^4*e^3*c^2*b+e^4*a^3*b^2*c-e^4*a^3*b^2*d-e^4*a^3*c^2*b+e^4*a^3*c^2*d+e^4*a^3*d^2*b-e^4*a^3*d^2*c-e^4*b^3*a^2*c+e^4*b^3*a^2*d+e^4*b^3*c^2*a-e^4*b^3*c^2*d-e^4*b^3*d^2*a+e^4*b^3*d^2*c+e^4*c^3*a^2*b-e^4*c^3*a^2*d-e^4*c^3*b^2*a+e^4*c^3*b^2*d+e^4*c^3*d^2*a-e^4*c^3*d^2*b-e^4*d^3*a^2*b+e^4*d^3*a^2*c+e^4*d^3*b^2*a-e^4*d^3*b^2*c-e^4*d^3*c^2*a+e^4*d^3*c^2*b

radsimp:

combine(trig):

a^4*b^3*c^2*d-a^4*b^3*c^2*e-a^4*b^3*d^2*c+a^4*b^3*d^2*e+a^4*b^3*e^2*c-a^4*b^3*e^2*d-a^4*c^3*b^2*d+a^4*c^3*b^2*e+a^4*c^3*d^2*b-a^4*c^3*d^2*e-a^4*c^3*e^2*b+a^4*c^3*e^2*d+a^4*d^3*b^2

共6页:

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