Is this DE linear?

  • Thread starter cocopops12
  • Start date
30
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(y^2)'' + (y^2)' + y^2 = 0

1) Is this DE linear?

What if we substitute y^2 = h
and solve for h
y = sqrt(h)

2) Would that be valid?
3) Would that be considered a somewhat trivial type of linearization?
 

rbj

2,221
7
if you make that substitution, it's linear.
 
315
0
cocopuff,

Is this DE linear?

--------------------------------------------------------------------------------
(y^2)'' + (y^2)' + y^2 = 0
No, of course not. The dependent variable is "y" and y^2 is nonlinear.

What if we substitute y^2 = h
and solve for h
y = sqrt(h)

2) Would that be valid?
Yes.

3) Would that be considered a somewhat trivial type of linearization?
No, linear DE's are not classified as trivial linear or nontrivial linear DE's.

Ratch
 

pasmith

Homework Helper
1,735
408
(y^2)'' + (y^2)' + y^2 = 0

1) Is this DE linear?

What if we substitute y^2 = h
and solve for h
y = sqrt(h)

2) Would that be valid?
Yes.

If you want y to be real-valued, then you will need [itex]h(t) \geq 0[/itex] for all t. Unfortunately the general solution of that particular ODE is oscillatory with a decaying amplitude, so there will be intervals where [itex]h(t) < 0[/itex] unless [itex]h(t) = 0[/itex] for all t.
 

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