Why matlab only fives one complex result?
2 views (last 30 days)
Show older comments
Graciano Ding
on 30 Oct 2019
Commented: Graciano Ding
on 30 Oct 2019
Hello everyone, I have been struggling for so much time...I have been doing a complex equation (I am actually able to solve it manually but I just want to ger more familiar with Matlab). There are 3 complex solutons, however, matlab only gives me one of them. What can I do so that it gives me all 3 solutions?
0 Comments
Accepted Answer
Walter Roberson
on 30 Oct 2019
Square both sides of the equation. MATLAB will provide 3 solutions.
It is advisable to cross check the solutions, as squaring both sides can introduce false roots.
2 Comments
Walter Roberson
on 30 Oct 2019
>> syms z
>> solve((z^(-3/2))^2 == (3-3*i)^2)
ans =
(1i/18)^(1/3)
(1i/18)^(1/3)*((3^(1/2)*1i)/2 - 1/2)
-(1i/18)^(1/3)*((3^(1/2)*1i)/2 + 1/2)
>> simplify(solve((z^(-3/2))^2 == (3-3*i)^2))
ans =
((-1)^(1/6)*18^(2/3))/18
((-1)^(1/6)*2^(2/3)*3^(1/3)*(- 1 + 3^(1/2)*1i))/12
-((-1)^(1/6)*2^(2/3)*3^(1/3)*(1 + 3^(1/2)*1i))/12
>> double(ans)
ans =
0.330450538041682 + 0.190785707092222i
-0.330450538041682 + 0.190785707092222i
0 - 0.381571414184444i
>> ans.^(-3/2)
ans =
3 - 3i
-3 + 3i
-3 + 3i
Cross-check shows there is only one solution. The claim that there are 3 solutions is incorrect.
More Answers (1)
Sai Bhargav Avula
on 30 Oct 2019
Edited: Sai Bhargav Avula
on 30 Oct 2019
Hi,
MATLAB cannot generate all the Solutions, which might require a global solver.
However, if you have the Extended Symbolic Math Toolbox (access to Maple), then you can do this in Maple.
maple('_EnvAllSolutions:= true;')
This can give a generic result for the equation provided
2 Comments
Walter Roberson
on 30 Oct 2019
This is misleading. Producing all of the solutions does not require a global solver.
Sai Bhargav Avula
on 30 Oct 2019
It might require different intilizations to get all the solutions. So I suggested this.
See Also
Categories
Find more on Symbolic Math Toolbox in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!