[MATLAB数学相关] 求积分问题

[ironman]

遇到问题了，请高手帮帮忙了~~



下面这是我做的图像，现在我想求积分，就是曲线与横坐标之间的面积，不知怎么求？

不可以用int（a,n）吗？


n=[600:4000];

u=0.0043*n;
Tq=-19.313+295.27*(n/1000)-165.44*(n/1000).^2+40.874*(n/1000).^3-3.8445*(n/1000).^4;
Ft=75.0751*Tq;

Fw=512173/211500000000*n.^2;

a=5365.652./(Ft-300.7580-Fw);

plot(u,a)

[ironman]

没有人知道么？
这个问题把我卡住了，作业没法继续。。。

[tp4411]

作者: ironman

没有人知道么？
这个问题把我卡住了，作业没法继续。。。

我觉得，int函数 是积f(x)的函数 ，你这是矩阵啊！我是这么想的

[mouse_yy]

首先画图，然后，设置n为变量，对a ,在【600，4000】内函数求积分；
n=[600:4000];

u=0.0043*n;
Tq=-19.313+295.27*(n/1000)-165.44*(n/1000).^2+40.874*(n/1000).^3-3.8445*(n/1000).^4;
Ft=75.0751*Tq;

Fw=512173/211500000000*n.^2;

a=5365.652./(Ft-300.7580-Fw);

plot(u,a)%绘图完成

%如果在这里直接使用 syms n;f=int(a,n,600,4000)将会得到一个矩阵，估计你不想看见
%按照下面这样处理之后将得到一个很复杂的表达式

syms n;

Tq=-19.313+295.27*(n/1000)-165.44*(n/1000).^2+40.874*(n/1000).^3-3.8445*(n/1000).^4;
Ft=75.0751*Tq;

Fw=512173/211500000000*n.^2;

a=5365.652./(Ft-300.7580-Fw)

f=int(a,n,600,4000)


%结果为
a =

-2949798382299775/(549755813888*((40620529550730443127*n^4)/140737488355328000000000000000 - (107967455121378341291*n^3)/35184372088832000000000000 + (11458053194332167757187849*n^2)/922337203685477580800000000 - (155989384321032357161*n)/7036874417766400000 + 123193392754006110959/70368744177664000))




Fr =

386635973564796108800000000000000000*sum(b*log(367879934790086244340835454993508319710749316304853065930446914646855407055392272949218750000*b^3 + 2386264125144221325978691907032893240337946042169803998046875*b^2 + 1196707861222750468402077696*b), b in RootOf(_X^4 - 212219074014486054320300028260960552545613984764528462316916569165307437190391/3837013279033630849309124168425994764491494654313871515744978258920045816813987986162624881276583333279042435228903337161361088000000000000000000*_X^2 - 33614207733540331107729134038071468852974309621/457407626990512710727348824551820130883633453168138446300623209347730376340626238127067670974324146900062851337063710351152549743652343750000000000*_X - 3154861128440064416197/12705767416403130853537467348661670302323151476892734619461755815214732676128506614640768638175670747223968092696214176420904159545898437500000000000000000, _X)) - 386635973564796108800000000000000000*sum(b*log(29536384196222047165956391774625377403143054899191025058799567550828278283189697265625000000*b^3 + 389479405795023752607236066606366428598702691151605599609375*b^2 - 156081149927419324091117568*b), b in RootOf(_X^4 - 212219074014486054320300028260960552545613984764528462316916569165307437190391/3837013279033630849309124168425994764491494654313871515744978258920045816813987986162624881276583333279042435228903337161361088000000000000000000*_X^2 - 33614207733540331107729134038071468852974309621/457407626990512710727348824551820130883633453168138446300623209347730376340626238127067670974324146900062851337063710351152549743652343750000000000*_X - 3154861128440064416197/12705767416403130853537467348661670302323151476892734619461755815214732676128506614640768638175670747223968092696214176420904159545898437500000000000000000, _X))

至于这个结果中的一些东西，自己研究，太复杂了，

[ironman]

恩，谢谢你~
这个结果昨天我也得出来了
不知能不能把结果近似一下呢？我只想要个简单的近似值，最多精确两位小数就行。该怎么办呢？