# How can i make my ODE graph make sense?

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Ian Samuelsson on 18 Oct 2021
Commented: Star Strider on 18 Oct 2021
I don't know why my graph is like that ! I tried to plot the differential and the solved ODE but my graph dont make sense.
I'm trying to make a graph of a ODE about a ball dropping in oil, the values are all random, just to plot the thing
clear; clc;
clearvars;
syms t v(t) aa g p p1
aa = 5;
u = 3;
g = 10
p1 = 9;
p = 3;
v0= 0;
cond = v(0) == v0
eqn = diff(v,t) == (1-p1/p)*g-(9*u/2*aa^2*p)*v
vSol(t)= simplify( dsolve(eqn,cond) )
fplot(t,vSol(t),[0 10000]); hold on; grid on;
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### Accepted Answer

Star Strider on 18 Oct 2021
The fplot call is incorrect, and the function declines so quickly that it’s not possible to see it clearly with a time interval going from 0 to 1E+5.
Correct those and it works!
syms t v(t) aa g p p1
aa = 5;
u = 3;
g = 10
g = 10
p1 = 9;
p = 3;
v0= 0;
cond = v(0) == v0
cond =
eqn = diff(v,t) == (1-p1/p)*g-(9*u/2*aa^2*p)*v
eqn(t) =
vSol(t)= simplify( dsolve(eqn,cond) )
vSol(t) =
figure
fplot(vSol(t),[0 1E-2]); hold on; grid on;
.
##### 8 CommentsShowHide 7 older comments
Star Strider on 18 Oct 2021
The hold condition can be toggled on or off depending on whether other data are to be plotted to the same axes, or not.

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