Hey, I have a system of ODE and I can't draw it's phase curve. I tried to use DEplot and phaseportrait, but it doesn't work. Here is my system:

 dx/dt=x

dy/dt=ky              (k is a constant)

Here is my piece of code:

DE := [diff(x(t), t) = x(t)];

DF := [diff(y(t), t) = k*y(t)];

with(DEtools);

phaseportrait([DE, DF], [y, x], t = -5 .. 5, y = -5 .. 5, x = -5 .. 5, k...

Hey, I'm trying to plot the phase curve of the simple system of ODE, BUT it shows me an error which one I don't understand at all :)

Here is my code:

DE := diff(x(t), t) = x(t);
DF := diff(y(t), t) = k*y(t);
with(DEtools);
phaseportrait([DE, D], [y, x], t = -5 .. 5, [[y(0) = 1, x(0)], [y(0) = 0, x(0) = 2], [y(0) = 0, z(0) = -2]], y = -5 .. 5, x = -5 .. 5, color = black, linecolor = red);

Error, (in DEtools/phaseportrait) invalid initial...

Hello, I have a problem with plotting graphs with a constant.. I have one system of equations and one another equation:

dx/dt=x(t)

dy/dt=ky(t)

and 

|y|=C|x|^k

I need to compare theit curves.

k and C are constants. I thought it is alright if I would remove constants, BUT there is one in the power, so I have no idea what to do.. 

I just tried to plot the system, but it doesn't work either:

Hello, I have a problem in plotting the vector field of dx/dt=sinx/sint

It shows me an error:

Error, (in DEtools/dfieldplot) unable to evaluate function `sin(x)` in evalhf

Dunno how to fix it

Here is my code:

DE := [diff(x(t), t) = sin(x)(t)/sin(t)];
with(DEtools):
DC:=[sin(x)/sin(t),.1]:
dfieldplot(DE, x(t), t = -2 .. 2, x = -1 .. 2, arrows = medium, title = 'Diff', color = DC);