## Apps.2ndOrderDifferential History

February 06, 2020, at 03:24 PM by 12.45.189.170 -
(:toggle hide gekko button show="Show GEKKO (Python) Code":)
(:div id=gekko:)
(:source lang=python:)
import numpy as np
from gekko import GEKKO
import matplotlib.pyplot as plt
m = GEKKO(remote=False)
m.time = np.arange(0,2.01,0.05)
K = 30
y = m.Var(2.0)
z = m.Var(-1.0)
t = m.Var(0.0)
m.Equation(t.dt()==1)
m.Equation(y.dt()==z)
m.Equation(z.dt()+(0.9+0.7*t)*z+K*y==0)
m.options.IMODE = 4; m.options.NODES = 3
m.solve(disp=False)
plt.plot(m.time,y.value,'r-',label='y')
plt.plot(m.time,z.value,'b--',label='z')
plt.legend()
plt.xlabel('Time')
plt.show()
(:sourceend:)
(:divend:)
February 06, 2020, at 03:08 PM by 12.45.189.170 -
Changed lines 17-18 from:
**Second Order ODE Example**
to:
'''Second Order ODE Example'''
Changed line 27 from:
**Modified Form for Solution**
to:
'''Modified Form for Solution'''
February 06, 2020, at 03:08 PM by 12.45.189.170 -
Changed lines 17-18 from:
Below is an example of a second-order differential equation with constant {K} and variable {y} with first derivative {y'} and second derivative {y''}:
to:
**Second Order ODE Example**

An
example of a second-order differential equation with constant {K} and variable {y} with first derivative {y'} and second derivative {y''}:

**Modified Form for Solution**
February 06, 2020, at 03:07 PM by 12.45.189.170 -
Changed lines 33-36 from:
A numerical solution to this equation can be computed with a variety of different solvers and programming environments. Solution files are available in MATLAB, Python, and Julia below or through a web-interface. Each of these example problems can be easily modified for solutions to other second-order differential equations as well.
to:
A numerical solution to this equation can be computed with a variety of different solvers and programming environments. Solution files are available in MATLAB, Python, and Julia below or through a web-interface.

Each
of these example problems can be modified for solutions to other second-order differential equations as well.
February 06, 2020, at 02:48 PM by 12.45.189.170 -
Changed lines 17-23 from:
Below is an example of a second-order differential equation.

-> Attach:2nd_order_ode.png

To numerically solve a differential equation
with higher-order terms, it can be broken into multiple first-order differential equations as shown below.

-> Attach
:2nd_order_ode_modified.png
to:
Below is an example of a second-order differential equation with constant {K} and variable {y} with first derivative {y'} and second derivative {y''}:

{$y''+(0.9+0.7t)y' + K\,y = 0$}

and with initial conditions
:

{$y(0)=2 \quad y'(0)=-1$}

To numerically solve a differential equation with higher-
order (such as 2nd derivative) terms, it can be broken into multiple first-order differential equations by declaring a new variable {z} and equation {z=y'}. The modified problem is then:

{$z'+(0.9+0.7t)z + K\,y = 0$}

and with initial conditions:

{$y(0)=2 \quad z(0)=-1$}
April 03, 2016, at 11:29 PM by 45.56.3.173 -
Changed lines 32-34 from:
Another scenario is when the damping coefficient ''c = (0.9 + 0.7 t)'' is not known but must be estimated from data. The value of ''c'' is allowed to change every 0.5 seconds. The true and estimated values of ''c'' are shown on the plot below. Predicted and actual values of ''y'' give excellent agreement.

Attach:2nd_order_differential_estimated.png
to:
Another scenario is when the damping coefficient ''c = (0.9 + 0.7 t)'' is not known but must be estimated from data. The value of ''c'' is allowed to change every 0.5 seconds. The true and estimated values of ''c'' are shown on the plot below. Predicted and actual values of ''y'' are in agreement even though the estimate is not continuous but only changes at discrete time points.

Attach:2nd_order_differential_estimated.png

April 03, 2016, at 11:28 PM by 45.56.3.173 -
Changed lines 30-34 from:
to:

Another scenario is when the damping coefficient ''c = (0.9 + 0.7 t)'' is not known but must be estimated from data. The value of ''c'' is allowed to change every 0.5 seconds. The true and estimated values of ''c'' are shown on the plot below. Predicted and actual values of ''y'' give excellent agreement.

Attach:2nd_order_differential_estimated.png
April 01, 2016, at 12:43 AM by 10.10.151.70 -
Changed line 1 from:
(:title Solve 2nd Order ODE:)
to:
(:title Solve 2nd Order Differential Equations:)
April 01, 2016, at 12:42 AM by 10.10.151.70 -

(:html:)
<iframe width="560" height="315" src="https://www.youtube.com/embed/JLtRK4Z1tEg" frameborder="0" allowfullscreen></iframe>
(:htmlend:)
March 31, 2016, at 11:46 PM by 10.5.113.123 -
Changed line 19 from:
-> Attach:2nd_order_ode.png
to:
-> Attach:2nd_order_ode_modified.png
March 31, 2016, at 11:46 PM by 10.5.113.123 -
Changed lines 17-19 from:
A numerical solution to this equation can be computed with a variety of different solvers and programming environments. Solution files are available in Julia, MATLAB, and Python below or through a web-interface. Each of these example problems can be easily modified for solutions to other differential equations as well.

to:
To numerically solve a differential equation with higher-order terms, it can be broken into multiple first-order differential equations as shown below.

-> Attach:2nd_order_ode.png

A numerical solution to this equation can be computed with
a variety of different solvers and programming environments. Solution files are available in MATLAB, Python, and Julia below or through a web-interface. Each of these example problems can be easily modified for solutions to other second-order differential equations as well.
March 31, 2016, at 11:35 PM by 10.5.113.123 -
Changed line 15 from:
Attach:2nd_order_ode.png
to:
-> Attach:2nd_order_ode.png
March 31, 2016, at 07:47 PM by 10.5.113.123 -
A differential equation relates some function with the derivatives of the function. Functions typically represent physical quantities and the derivatives represent a rate of change. The differential equation defines a relationship between the quantity and the derivative. Differential equations are very common in fields such as biology, engineering, economics, and physics.

Attach:2nd_order_ode_solution.png

Differential equations may be studied from several different perspectives. Only simple differential equations are solvable by explicit formulas while more complex systems are typically solved with numerical methods. Numerical methods have been developed to determine solutions with a given degree of accuracy.

The term with highest number of derivatives describes the order of the differential equation. A first-order differential equation only contains single derivatives. A second-order differential equation has at least one term with a double derivative. Higher order differential equations are also possible.

Below is an example of a second-order differential equation.

Attach:2nd_order_ode.png

A numerical solution to this equation can be computed with a variety of different solvers and programming environments. Solution files are available in Julia, MATLAB, and Python below or through a web-interface. Each of these example problems can be easily modified for solutions to other differential equations as well.