## where did the 3 come from? dsolve question....

The solution by Maple below is correct, but non-the-less, a little strange.

```restart;
dsolve(diff(y(x),x)=3*x^2*(y(x)^2+1),y(x));
```

Gives

Ofcourse 3*constant is still constant. But it is a little strange and have no reason for it to be there.  When I solve it by hand

What could made Maple put the 3 in there? Again, solution is 100% correct, but it could be simpler.

Maple 2017.1

## problem with simple ODE...

Dear Community,

I try to solve the following very simple ODE symbolically with the ODE Analyzer assistant, yet Maple says "unble to obtain solution". :-/

If I try to slove it with dsolve, nothing happens. Is it really so difficult?

diff(p(h),h)=A/(B+C*p(h)), p(h0)=p1

A, B, C, h0 and p1 are constants. I use Maple 2016.

best egards

Andras

## How to solve and plot system differential equation...

How to solve this problem? I want to display plot of differential equation system

Thank you :)

## why dsolve solution sometimes shows as implicit wh...

Sometimes dsolve returns solution as implicit, even when not using the `implicit` option. For example

```restart;
ode:=diff(y(x),x)=(x*y(x))^(1/2):
sol:=dsolve(ode,y(x));```

Gives

Which is the same result if I had used 'implicit'.

Is there a way to tell dsolve not to do this? is it becuase it can't solve for y(x) from the above?

Maple 2017.1

## how can i draw a plot rkf45 ...

i want to draw plot Y[1] . but i cant. thank you

restart;
with(LinearAlgebra); Digits := 15; with(plots); with(Optimization);;
NewM := Matrix(5, 5, [[4119700.0000, 0., 0., 0., 0.], [0., 175900.0000, 0., 0., 0.], [0., 0., 52796., 0., 0.], [0., 0., 0., 2002900.0000, 0.], [0., 0., 0., 0., 21711.]]); NewK := Matrix(5, 5, [[18278000.0000, 0., 0., 0., 0.], [0., 8478500.0000, 0., 0., 0.], [0., 0., 3874800.0000, 0., 0.], [0., 0., 0., 494710000.0000, 0.], [0., 0., 0., 0., 7707500.0000]]); L := Vector[column](5, [400689.480747934, 36882.2103608425, 24223.1756570268, 7197.48654698287, 5007.64668721342]); V := Vector[column](5, [4.43679672962542, 48.2014976972537, 73.3916065733549, 246.999805581163, 355.012621460930]);
Phi := Matrix(5, 5, [[1., 1., 1., 1., 1.], [1.96506022575420, 1.62041320563413, 1.42204109823483, 0.548765310483432e-1, -.795724394004826], [9.21473910149806, 2.36597630710861, -.837387679777313, -8.23805381555997, 0.930594200639915e-1], [10.5672146719479, 1.26937656539014, -.710851068914949, 12.5801876194058, -0.564138989400088e-1], [12.4282433098880, -2.02516824673162, .481291188486771, -1.71479964168293, 0.513709374343217e-2]]);
NS := ImportMatrix("D:/tabas.txt", datatype = float[8]);
t_NS := NS[() .. (), 1];
acc_NS := NS[() .. (), 2];
plot(NS, t = 0 .. 4.5, size = [800, 400]);
acc := unapply(CurveFitting:-Spline(t_NS, acc_NS/(9.81), t, degree = 1), t);
eq := seq(diff(x[i](t), t\$2)+(2*0.5e-1)*sqrt(V[i])*(diff(x[i](t), t))+V[i]*x[i](t) = L[i]*acc(t)/NewM[i, i], i = 1 .. 5, 1);
ic := [seq({x[i](0) = 0, (D(x[i]))(0) = 0}, i = 1 .. 5, 1)];
sol := seq(dsolve({eq[i], ic[i][]}, numeric, output = listprocedure), i = 1 .. 5, 1);
Z := `<,>`(seq(sol[i][2], i = 1 .. 5));
#Y := Phi . Z;
#odeplot(Y[1], t = 0 .. 10);
tabas.txt

1.mw

## how can i draw odeplot this numeric dsolve...

i want to draw plot Y[1] . but i cant. thank for you

i want to take this equation

restart;
with(LinearAlgebra); Digits := 70; with(plots);

K := Matrix(5, 5, [[18278000.0000, 0., 0., 0., 0.], [0., 8478500.0000, 0., 0., 0.], [0., 0., 3874800.0000, 0., 0.], [0., 0., 0., 494710000.0000, 0.], [0., 0., 0., 0., 7707500.0000]]); M := Matrix(5, 5, [[4119700.0000, 0., 0., 0., 0.], [0., 175900.0000, 0., 0., 0.], [0., 0., 52796., 0., 0.], [0., 0., 0., 2002900.0000, 0.], [0., 0., 0., 0., 21711.]]); L := Vector[column](5, [400689.48, 36882.21, 24223.175, 7197.4865, 5007.6466]); V := Vector[column](5, [4.4368, 48.201, 73.39160, 246.999, 355.012]);
NS := ImportMatrix("D:/tabas.txt", datatype = float[8]);
t_NS := NS[() .. (), 1];
acc_NS := NS[() .. (), 2];
plot(NS, t = 0 .. 4.5, size = [800, 400]);
acc := unapply(CurveFitting:-Spline(t_NS, acc_NS/(9.81), t, degree = 1), t);
eq := seq(diff(x[i](t), t\$2)+(2*0.5e-1)*sqrt(V[i])*(diff(x[i](t), t))+V[i]*x[i](t) = L[i]/M[i, i], i = 1 .. 5, 1);
ic := [seq({x[i](0) = 0, (D(x[i]))(0) = 0}, i = 1 .. 6, 1)];
res := evalf(seq(dsolve({eq[i], ic[i][]}, numeric, method = rkf45), i = 1 .. 5, 1));
Z := `<,>`(res[1], res[2], res[3], res[4], res[5]);
Y := Phi . Z;
#odeplot(rhs(Y[1]), t = 0 .. 4)

import file text

tabas.txt

## how can i solve maximize of numerical dsolve...

restart;
res := dsolve({25*(diff(y(t), t, t))+4*(diff(y(t), t))-3*y(t) = cos(3*t), y(0) = 0, (D(y))(0) = 1}, numeric, method = rkf45);
with(Optimization);
Maximize(res, t = 0 .. 4);

## "unable to store %1 when datatype=%2", -9.65986559...

hello...how i can remove this error?

thanks

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