Incorrect Calculation when using symunit in Symbolic Math Toolbox

2023 11 29
1 个回答
回答已采纳
更新时间：2023 12 11
8 次查看（30 天）

0 个投票

clc,clear
syms x a
u = symunit;
a = 1.01325*u.bar
b = -0.049576382*u.bar*u.m^3/u.mol
c = .000003657553277*u.bar*u.m^6/(u.mol)^2
d = -.00000000015676624*u.bar*u.m^9/u.mol^3
eqn = a*x^3+b*x^2+c*x+b == 0
solve(eqn,x,"MaxDegree",3)
vpa(solve(eqn,x,'MaxDegr
Output: 0.016
clc,clear
syms x
u = symunit;
a = 1.01325
b = -0.049576382
c = 3.657553277*10^-6
d = -1.5676624*10^-10
eqn = a*x^3+b*x^2+c*x+b == 0
solve(eqn,x,"MaxDegree",3)
vpa(solve(eqn,x,'MaxDegree',3),10)
Output: 0.382
a = 1.01325
b = -0.049576382
c = 3.657553277*10^-6
d = -1.5676624*10^-10
x = [a b c d];
vpa(roots(x),10)
Output: 0.048
u = symunit;
a = 1.01325*u.bar
b = -0.049576382*u.bar*u.m^3/u.mol
c = .000003657553277*u.bar*u.m^6/(u.mol)^2
d = -.00000000015676624*u.bar*u.m^9/u.mol^3
x = [a b c d];
vpa(roots(x),10)
Output: root(z^3 - ((sym("223272175501577375")*z^2)/sym("4563272322433155072"))*(symunit("m")^3/symunit("mol")) + ((sym("539759593894213625")*z)/sym("149529307461489625399296"))*(symunit("m")^6/symunit("mol")^2) - sym("252691673573204875/1633258782299364015028043776")*(symunit("m")^9/symunit("mol")^3), z, 1)
Wolfram Alpha Answer: 0.048

2 个评论
显示 无 隐藏 无

Dyuman Joshi
Dyuman Joshi 2023-11-29
Ran in:
Ran in:
Where exactly do you get the output 0.016 from the first snippet of code?
Do you mean the sigma2 value? If yes, then you are misunderstanding the solution. The solutions are the elements of the 3x1 vector, where the terms have been grouped. And the information below the solutions show, which terms have been grouped into the respective variables.
Also, there's a mistake in the 2nd piece of code, you have written a*x^3 + b*x^2 + c*x + b == 0, it should be d instead of b. Correcting the mistake leads to the correct output, see below -
clc,clear
syms x a
u = symunit;
a = 1.01325*u.bar;
b = -0.049576382*u.bar*u.m^3/u.mol;
c = .000003657553277*u.bar*u.m^6/(u.mol)^2;
d = -.00000000015676624*u.bar*u.m^9/u.mol^3;
eqn = a*x^3+b*x^2+c*x+b == 0
eqn = 
vpa(solve(eqn,x,"MaxDegree",3), 10)
ans = 
clc,clear
syms x
u = symunit;
a = 1.01325;
b = -0.049576382;
c = 3.657553277*10^-6;
d = -1.5676624*10^-10;
% v
eqn = a*x^3+b*x^2+c*x+d == 0;
solve(eqn,x,"MaxDegree",3);
vpa(solve(eqn,x,'MaxDegree',3),10)
ans = 
clear
a = 1.01325;
b = -0.049576382;
c = 3.657553277*10^-6;
d = -1.5676624*10^-10;
x = [a b c d];
vpa(roots(x),10)
ans = 
u = symunit;
a = 1.01325*u.bar;
b = -0.049576382*u.bar*u.m^3/u.mol;
c = .000003657553277*u.bar*u.m^6/(u.mol)^2;
d = -.00000000015676624*u.bar*u.m^9/u.mol^3;
x = [a b c d];
vpa(roots(x),10)
ans = 
Breyonna
Breyonna 2023-12-11
First of all, thank you SO much. I really appreciate the solution. Do the units negate the calculation? Is it possible to get the numerical output from the code without units into the output with the code with units.
I am basically punching in numbers without understanding the output at this point.
clc,clear
syms x
u = symunit;
a = 1.01325*u.bar;
b = -0.049576382*u.bar*u.m^3/u.mol;
c = .000003657553277*u.bar*u.m^6/(u.mol)^2;
d = -.00000000015676624*u.bar*u.m^9/u.mol^3;
% v
eqn = a*x^3+b*x^2+c*x+d == 0;
solve(eqn,x,"MaxDegree",3);
vpa(solve(eqn,x,'MaxDegree',3),10)
I am trying to figure out how to output 0.048 m^3/mol for the above code.
I don't know how to ask it to do that.

请先登录，再进行评论。

请先登录，再回答此问题。

 采纳的回答

Breyonna
Breyonna 2023-12-11
移动：Dyuman Joshi 2023-12-11

0 个投票

Got it......somehow. Thanks again.
clc,clear
syms x
u = symunit;
a = 1.01325*u.bar;
b = -0.049576382*u.bar*u.m^3/u.mol;
c = .000003657553277*u.bar*u.m^6/(u.mol)^2;
d = -.00000000015676624*u.bar*u.m^9/u.mol^3;
% v
eqn = a*x^3+b*x^2+c*x+d == 0;
vpa(simplify(solve(eqn, x, 'maxdegree', 3)))
ans =

更多回答（0 个）

类别

在 帮助中心 和 File Exchange 中查找有关 Function Creation 的更多信息

产品

版本

R2023b

标签

Community Treasure Hunt

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

Start Hunting!

Translated by