I could not integrate using MatLab, Can you please help me?

syms t a c
fun = 3*2^(1/2)*(1 - cos(4*t))^(1/2)*(a^2 + c^2)^(1/2);
z = int(fun,t); %gives indefinite integral
%result of integration, z = -(3*sin(4*t)*(a^2 + c^2)^(1/2))/(2*(sin(2*t)^2)^(1/2));
t=0;
res = z - subs(z); 
%obtain final result by evaluating the integral, z(t)-z(0), by assigning t & using subs()

However, you will not get the result. See @Walter Roberson's comment below for more details.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Walter Roberson 2021-5-5

编辑：Walter Roberson 2021-5-5

在 MATLAB Online 中打开

Not quite.

syms t a c

fun = 3*2^(1/2)*(1 - cos(4*t))^(1/2)*(a^2 + c^2)^(1/2);

z = int(fun,t); %gives indefinite integral

char(z)

ans = '-(3*sin(4*t)*(a^2 + c^2)^(1/2))/(2*(sin(2*t)^2)^(1/2))'

z0 = limit(z, t, 0, 'right');

char(z0)

ans = '-3*(a^2 + c^2)^(1/2)'

res = simplify(z - z0);

char(res)

ans = '3*(a^2 + c^2)^(1/2) - (3*sin(4*t)*(a^2 + c^2)^(1/2))/(2*(sin(2*t)^2)^(1/2))'

fplot(subs(z, [a,c], [1 2]), [-5 5])

fplot((subs(fun,[a,c], [1 2])), [-5 5])

That is, the problem is that the integral is discontinuous at t = 0 and that is why int() cannot resolve it.

请先登录，再进行评论。

Answer 2

Walter Roberson 2021-5-5

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/819725-i-could-not-integrate-using-matlab-can-you-please-help-me#answer_692855

在 MATLAB Online 中打开

syms a c t real

mag_dr = 3*2^(1/2)*(1 - cos(4*t))^(1/2)*(a^2 + c^2)^(1/2)

mag_dr =

z = int(mag_dr, t)

z =

z - limit(z, t, 0, 'right')

ans =

The integral is discontinuous at 0, which is why it cannot be resolved by MATLAB.

4 个评论
显示 2更早的评论隐藏 2更早的评论

Dyuman Joshi 2021-5-6

The wrong substitution was a mistake on my part, mostly cause I did it in a hurry. I have edited my nswer accordingly as well. Other than that, is subs() a good approach or would you recommend otherwise?

Walter Roberson 2021-5-6

limit() is more robust than subs() for cases like this. But limit() is sometimes quite expensive to calculate, or is beyond MATLAB's ability to calculate, even in some finite cases.

请先登录，再进行评论。

Answer 3

Sindhu Karri 2021-5-5

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/819725-i-could-not-integrate-using-matlab-can-you-please-help-me#answer_692475

Hii

The "int" function cannot solve all integrals since symbolic integration is such a complicated task. It is also possible that no analytic or elementary closed-form solution exists.

For definite integrals, a numeric approximation can be performed by using the "integral" function.