Problem using the 'subs' command(Error using symengine)

20 次查看（过去 30 天）
Jen Cong Wong
Jen Cong Wong 2017-12-11
回答： Birdman 2017-12-12
I am trying to solve the cubic equation 0.75*k*B1^3 -m*w^2*B1 + c*B1 - A == 0 and get the absolute number for the roots. However, I encounter "Error using symengine" when I try to use replace the 'k' symbolic variable with 0 using 'subs' command. Below is my code. There is no problem if I enter some value other than 0 in the code.
syms A m c k w B1
eqn = 0.75*k*B1^3 -m*w^2*B1 + c*B1 - A == 0
sol = solve(eqn,B1)
root = abs(subs(sol, [k,m,c,A], [0,1,1,1]))
And below is the errors that I got:
Error using symengine The third argument must be an integer between 1 and the degree of the polynomial.
Error in sym/subs>mupadsubs (line 140) G = mupadmex('symobj::fullsubs',F.s,X2,Y2);
Error in sym/subs (line 125) G = mupadsubs(F,X,Y);
Error in NonlinearStudy (line 9) root = abs(subs(sol, [k,m,c,A], [0,1,1,1]))

请先登录，再回答此问题。

采纳的回答

Birdman
Birdman 2017-12-12
You should use subs command for coefficients before solving the equation.
syms A m c k w B1
eqn = 0.75*k*B1^3 -m*w^2*B1 + c*B1 - A == 0
eqn = subs(eqn,{k,m,c,A},{0,1,1,1})
sol = solve(eqn,B1)

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Conversion Between Symbolic and Numeric 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by