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Plot the direction field on
SLOPES
using a window [-2,+2]x[-2,+5].
Make a hard copy of the said direction field. Look for a GLOBAL
pattern in the direction field as well as LOCAL patterns in
various regions of the solution plane:
Do you see solution curves on the plane that serve like
asymptotes (spine) or "attractors" for the other solution curves
nearby ? Do you also see regions where each solution curve
"goes" its own way without being attracted to other solution
curves in the vicinity ? Do you see any lines that serve as
vertical or horizontal asymptotes for ALL solution curves on the
solution plane ? Mark your observations on the hard copy by hand,
showing lines, curves, and regions with the mentioned behavior
patterns.
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Plot several solution curves on the direction field on
SLOPES
to
test/investigate your observations in Part-1. Try to put as many
integral curves as you see fit in various parts of the solution
plane for an exhaustive analysis of the entire solution space
without crashing the software. Make a new hard copy of the screen
with all the integral curves on it. It may be a good idea to make
two hard copies of the integral curves; one with the direction
field in the background and one without.
Mark the key features, mentioned in Part-1, of the solution family
on the hard copy by hand.
-
Repeat Part-1 and Part-2 for a window [-1,+1]x[-1,+1], focusing on
the region near (0,0). Keep looking for a "spine" that behaves
like an attractor (asymptote).
-
The ODE has a SINGULARITY at x=0, that is,
the ODE "blows up", since the coefficient (2x+1)/x becomes undefined,
when x=0. How does this feature of the ODE display itself in the
topology of the solution space ? How do the solution curves BEHAVE as
they come near the region(s) where x=0 ? How do you explain this
behavior through (a) the ODE itself, (b) the general solution ?
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Now go to
TWIDDLE
and create a generic function f(x;c)
representing the one-parameter family of solutions (the general
solution) for the ODE. Using a window [-1,+2]x[-0.5,+0.5] draw a
sufficient number of solution curves for various values
(negative,zero,positive) of the parameter "c". Make a hard copy
of the screen. Mark the c-value for each curve by hand on the
hard copy. Comment on the curve for c=0. How does this curve
(c=0) relate to your observations in Parts~1-3 above ? Please
explain. Can you write the equation of this special curve ? Does
this curve belong to the solution family of the DE ? Does the
equation of this curve satisfy the ODE itself ? Does this curve
fit into the direction field for the ODE ?
Please comment on these and similar questions.
The solution curves created on
TWIDDLE
using the closed-form
expression for the solution family should naturally fit into the
direction field for the ODE, as well as all the integral curves
created on
SLOPES
in Part-1, Part-2 and Part-3. Please comment on
this anticipated correspondence.
-
Address the questions raised in Part-4 using the graphs made
on
TWIDDLE
. Do your observations match your findings in Part-4 ?
Please comment.
-
Repeat the analysis in Part-1 by zooming in on a much smaller
window [-0.01,+0.01]x[-0.01,+0.01] to see if the global
characteristics of the direction field are preserved at the local
level around (0,0). Follow the same procedure as in Part-1.
-
What can you conclude about the impact of the singularity at
x=0 in shaping the geometry of the solution curves in the
vicinity of the singularity ? How does the spine at c=0 fit into
this general picture ? Please explain.
You may find it useful to zoom out and look at the direction
field over a window [-2,+2]x[-4,+12] to see the BIG PICTURE away
from (0,0) to answer this part.