MATLAB help (finding all the possible values for x)?

조회 수: 4 (최근 30일)
Tristan
Tristan 2013년 9월 5일
Hi, I'm new to MATLAB,
I need to find all the possible values for x knowing that:
0<x<10
and
1.8*cos(1.8*x)+1.2*cos(1.2*x)=0
the only thing that works is
>> evalin(symengine, 'numeric::solve(1.8*cos(1.8*x)+1.2*cos(1.2*x)=0, x = 0..10)')
ans =
1.0057538744094438603875879163721
but it only gives one of the possible answers.
I should be getting
x≈
1.00575
2.97903
4.6645
5.80748
7.49295
9.46622
thanks

채택된 답변

Shashank Prasanna
Shashank Prasanna 2013년 9월 5일
syms x
x = solve(1.8*cos(1.8*x)+1.2*cos(1.2*x))
This gave me the analytical solution.
A more feasible way would be to solve this numerically using MATLAB:
x = fsolve(@(x)1.8*cos(1.8*x)+1.2*cos(1.2*x),10*rand(1))
Each time you run this you will get one of the different results. The second argument asks FSOLVE to start solving from a different start point.

추가 답변 (1개)

Roger Stafford
Roger Stafford 2013년 9월 5일
Another approach is to expand both cosines in terms of cos(.6*x) which gives a cubic equation in the quantity. Any of its roots which are real and between -1 and +1 will give you an arccosine equation from which you can find all the solutions in the range you state.

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