Differential Equations Problem
02-14-2017, 06:07 PM
Post: #1
 Eddie W. Shore Senior Member Posts: 1,289 Joined: Dec 2013
Differential Equations Problem
I received an email with the question:
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I am trying to solve the simplest first order ode I could think of:

dy/dx - 4y = 0 for y(0) = 1

the solution should be y(x) = y(0) e^4x

I tried

plotode(4*y, [y], [1])

but I just get the error message "bad argument type".

I thought perhaps I need to give it the independent variable, so I tried

plotode(4*y, [x,y], [0,10)

which now runs, but it makes a vertical line straight up.
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I have tried to use both odesolve and desolve with no success.

odesolve(4*y, [x,y]) returns the same
odesolve(4*y, [x,y], [0,1]) returns Bad Argument Type
desolve(4*y, [x,y], [0,1]) returns [[ ]]
desolve(y' - 4*y = 0, [x,y], [0,1]) returns [[ ]]

Any help?
02-14-2017, 06:37 PM (This post was last modified: 02-14-2017 06:37 PM by Han.)
Post: #2
 Han Senior Member Posts: 1,883 Joined: Dec 2013
RE: Differential Equations Problem
desolve(y'-4*y=0 and y(0)=1)

Graph 3D | QPI | SolveSys
02-14-2017, 07:52 PM
Post: #3
 parisse Senior Member Posts: 1,203 Joined: Dec 2013
RE: Differential Equations Problem
exp(4*x) is increasing ... exponentially ... fast, plotode output is not surprising.
02-15-2017, 02:27 PM
Post: #4
 Eddie W. Shore Senior Member Posts: 1,289 Joined: Dec 2013
RE: Differential Equations Problem
(02-14-2017 06:37 PM)Han Wrote:  desolve(y'-4*y=0 and y(0)=1)

Thank you Han! You're the best.
02-16-2017, 05:13 PM
Post: #5
 Jan_D Member Posts: 69 Joined: Nov 2016
RE: Differential Equations Problem
There is no need to try how the input of plotode should look like, because imo the Help is clear in its examples in this respect.

Plotode is meant for the Geometry app, and when you enter the command in its Symbolic view you get a nice graph.

When you want to solve differential equations choose:

Toolbox – CAS – Solve – Differential Equation (desolve)
Or
Toolbox – CAS – Solve –ODE Solve (odesolve)

Also the Help of desolve and odesolve is clear in my opinion.
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