How can i solve these two equations simultaneously for A and B ?

Question

Asif Arshid 2016-8-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/301006-how-can-i-solve-these-two-equations-simultaneously-for-a-and-b

编辑： Asif Arshid 2016-8-27

I have a system of 16 equations with 4 integration constants (A, B, C and D) in each soil layer (4 layers) and each soil layer has 4 stress-strain equations. I need to solve them simultaneously for 16 constants.

Below is the simplified form of two equations, which i am trying to solve for A and B.

int(5*besselj(0,x)*besselj(1, 0.5*x)*x*(A+5) ,x,0,10) = 0;

int(5*besselj(0,x)*besselj(1, 0.8*x)*x*(A+B) ,x,0,10) = A;

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2016-8-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/301006-how-can-i-solve-these-two-equations-simultaneously-for-a-and-b#answer_232890

The multiply by (A+5) in the first equation leads to the trivial solution A=-5, zeroing the effect of the besselj .

You can substitute A into the second equation and then do a numeric solve, restriction your range for B from 5 onwards; the numeric solution turns out to be about B = 5.57463755753316

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Asif Arshid 2016-8-27

编辑：Asif Arshid 2016-8-27

Thank you Walter Roberson for your quick reply. During my hit and trials of different functions, I got "vpasolve", it helped to solve for the equations upto the precision i was looking for.

z1 = int(5*besselj(0,x)*besselj(1,0.8*x)*x*(A+5),x,0,10);

z2 = int(5*besselj(0,x)*besselj(1,0.7*x)*x*(A+B),x,0,10);

[A, B] = vpasolve([z1==0, z2==A], [A, B])

One can equate z1 and z2 to any constant, variable or even functions of A and B, it will give you the approximate solution with reasonable precision. Thanks a lot again.

请先登录，再进行评论。