Solving Inequalities with Matlab

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Dimitrios Anagnostou
评论： Walter Roberson 2023-3-27
I guess this is a frequent question here but the answers I have seen did not help me.
I want to solve the following inequality: |x-2| > 2|x+1|.
Manually, we get
In Mathematica there is the built-in function Reduce.
In[58]:= Reduce[Abs[x - 2] > 2 Abs[x + 1], x, Reals]
Out[58]= -4 < x < 0
With Matlab I get
>> version
ans =
'9.13.0.2105380 (R2022b) Update 2'
>> syms x real
>> solve(abs(x-2) > 2*abs(x+1), x)
ans =
-2
There is this answer here that uses Mupad's Solve function but apparently it does not work anymore.
https://fr.mathworks.com/matlabcentral/answers/94721-is-there-a-method-for-solving-inequalities-using-the-symbolic-math-toolbox-5-6-r2011a
Is there a way to use a Matlab function, not necessarily solve to get the correct domain? Thank you very much.

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采纳的回答

Dyuman Joshi
Dyuman Joshi 2023-3-27
Ran in:
You need to use 'ReturnConditions' as true to obtain the conditions on the solution
syms x real
sol=solve(abs(x-2) > 2*abs(x+1), x,'ReturnConditions',true)
sol = struct with fields:
x: x parameters: x conditions: x < 0 & -4 < x
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Steven Lord
Steven Lord 2023-3-27
Yes, on the documentation page for the solve function. This documentation page also includes an example, "Solve Inequalities", that shows its use.

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