# 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;

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; .
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.