Kelly Shepphard
Kelly Shepphard

Reputation: 133

Taylor series vs numeric solution of nonlinear DE in maple

I want to plot two graphs: numeric solution of DE and Taylor series approximation for DE given. I have

de := diff(y(x), x$2) = x+y(x)-y(x)^2;
cond := y(0) = -1, (D(y))(0) = 1;
stp := 0.1e-1;
a, b := -5, 30;
numpts := floor((b-a)/stp+1);
p := dsolve({cond, de}, y(x), numeric, stepsize = stp, output = listprocedure); 

Plotting eval gives weird vertical line, while I expect to obtain plot that seems to oscillate as x -> ∞. For Taylor series, I've tried f:=[seq(taylor(y(x),x=i,n),i=-5..30 by stp)]; but seems like it won't work in such a way. What can I do with it? Why does my plot differ from expected?

Upvotes: 0

Views: 101

Answers (1)

acer
acer

Reputation: 7271

restart;
kernelopts(version);

    Maple 2018.0, X86 64 LINUX, Mar 9 2018, Build ID 1298750

de := diff(y(x), x$2) = x+y(x)-y(x)^2:
cond := y(0) = -1, (D(y))(0) = 1:
stp := 0.1e-1:
a, b := -5, 30:
numpts := floor((b-a)/stp+1):

p := dsolve({cond, de}, y(x), numeric, stepsize = stp,
            output = listprocedure):

Y:=eval(y(x),p);

                Y := proc(x)  ...  end;

plot(Y, 0..20);

enter image description here

Order:=10:
S := convert(rhs(dsolve({cond, de}, {y(x)}, series)),polynom);

plot([S, Y(x)], x=0..1.5);

enter image description here

Order:=40:
S := convert(rhs(dsolve({cond, de}, {y(x)}, series)),polynom):

plot([S, Y(x)], x=0..2.0);

enter image description here

Upvotes: 1

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