MATLAB符号运算练习题.doc
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第五章符合运算练习题
1.求符号函数f=ax3+by2+cx+d分别对x,y进行三次微分;对y进行定积分和不定积分,对y的定积分区间为(0,1);对y趋向于1求极限。
>>symsxy
>>f=sym('a*x^3+b*y^2+c*x+d');
>>diff(f,x,3)
ans=
6*a
>>diff(f,y,3)
ans=
0
>>int(f,y,0,1)
ans=
a*x^3+c*x+b/3+d
>>int(f,y)
ans=
(b*y^3)/3+(a*x^3+c*x+d)*y
>>limit(f,y,1)
ans=
a*x^3+c*x+b+d
2.已知f=1/(1+x^2),g=sin(y),求复合函数f(g(y)).
>>symsxy
>>f=sym('1/(1+x^2)');
>>g=sym('sin(y)');
>>compose(f,g,x,y)
ans=
1/(sin(y)^2+1)
3.求三元非线性方程组的解。
>>f1=sym('x^2+2*x+1');
>>f2=sym('x+3*z-4');
>>f3=sym('y*z+1');
>>[x,y,z]=solve(f1,f2,f3)
x=
-1
y=
-3/5
z=
5/3
4.解方程组当y(0)=1,z(0)=0时,求微分方程组的解。
>>[y,z]=dsolve('Dy-z=cos(x),Dz+y=1','y(0)=1','z(0)=0','x')
y=
sin(x)/2+(x*cos(x))/2+1
z=
-(x*sin(x))/2
5.求级数和1+x+x2+…+xk+…的和。
>>symsk
>>symsum(1/(k^2),k,1,inf)
ans=
pi^2/6
>>symsxk
>>symsum(x^k,k,0,inf)
ans=
piecewise([1<=x,Inf],[abs(x)<1,-1/(x-1)])
6计算积分
>>f=sym('x^(1/2)/(1+x)^2');
>>int(f,1,inf)
ans=
pi/4+1/2
7计算积分
>>symsxz
>>f=sym('x/(1+z^2)');
>>int(f,z,1,inf)
ans=
(pi*x)/4
8求函数的5阶泰勒级数展开式
>>symsxa
>>f=sym('(1-2*x+x^3)^(1/2)-(1-3*x+x^2)^(1/3)');
>>taylor(f,x,a,'order',5)
ans=
(a^3-2*a+1)^(1/2)-(a-x)^4*(((5*(3*a^2-2)*((3*(a^3-2*a+1)^(1/2))/2-(3*(3*a^2-2)*(3*a*(a^3-2*a+1)^(1/2)-(3*a^2-2)^2/(4*(a^3-2*a+1)^(1/2))))/(4*(a^3-2*a+1))))/(6*(a^3-2*a+1))-(3*a^2-2)/(4*(a^3-2*a+1)^(1/2))+(3*a*(3*a*(a^3-2*a+1)^(1/2)-(3*a^2-2)^2/(4*(a^3-2*a+1)^(1/2))))/(2*(a^3-2*a+1)))/(4*(a^3-2*a+1))+((2*((2*(2*a-3)^2)/(9*(a^2-3*a+1)^(2/3))-(2*(a^2-3*a+1)^(1/3))/3))/(3*(a^2-3*a+1))+(8*(2*a-3)*((2*a-3)/(9*(a^2-3*a+1)^(2/3))-(5*((2*(2*a-3)^2)/(9*(a^2-3*a+1)^(2/3))-(2*(a^2-3*a+1)^(1/3))/3)*(2*a-3))/(6*(a^2-3*a+1))))/(9*(a^2-3*a+1)))/(4*(a^2-3*a+1)))-((3*a^2-2)/(2*(a^3-2*a+1)^(1/2))-(2*a-3)/(3*(a^2-3*a+1)^(2/3)))*(a-x)-(a^2-3*a+1)^(1/3)-(((2*a-3)/(9*(a^2-3*a+1)^(2/3))-(5*((2*(2*a-3)^2)/(9*(a^2-3*a+1)^(2/3))-(2*(a^2-3*a+1)^(1/3))/3)*(2*a-3))/(6*(a^2-3*a+1)))/(3*(a^2-3*a+1))+((3*(a^3-2*a+1)^(1/2))/2-(3*(3*a^2-2)*(3*a*(a^3-2*a+1)^(1/2)-(3*a^2-2)^2/(4*(a^3-2*a+1)^(1/2))))/(4*(a^3-2*a+1)))/(3*(a^3-2*a+1)))*(a-x)^3+(a-x)^2*((3*a*(a^3-2*a+1)^(1/2)-(3*a^2-2)^2/(4*(a^3-2*a+1)^(1/2)))/(2*(a^3-2*a+1))+((2*(2*a-3)^2)/(9*(a^2-3*a+1)^(2/3))-(2*(a^2-3*a+1)^(1/3))/3)/(2*(a^2-3*a+1)))
9.计算下列函数的倒数:
,求zx’,zy’。
>>symsxy
>>z=sym('x*exp(y)/(y^2)');
>>diff(z,x)
ans=
exp(y)/y^2
>>diff(z,y)
ans=
(x*exp(y))/y^2-(2*x*exp(y))/y^3