Python Syntax: Difference between revisions

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(Added a basic Python tutorial, cleaned up the page some. Will be back to clean up some more and improve upon the VPython tutorial itself.)
Line 1: Line 1:


Edited by Madelyn Hightower- Spring 2017  
Edited by Zach Sanchez - Fall 2017 (in progress)


==The Main Idea==
==The Main Idea==
This page discusses basic functioning of vPython and how the program can be used to produce models. While vPython is rather similar to the normal Python and uses the same syntax, vPython is an extension of Python and allows users to produce 3D models. It is frequently used for educational purposes, however it has also been used in research to help scientists visualize 3D models.  
VPython is an extension of the Python programming language that contains a 3D graphics module called Visual, which allows users to create simple simulations of physics problems. Its primary use is for educational purposes, although it has been used in research before in the past. We will use VPython on occasion to aid us in visualizing and experimenting with the ideas that we learn in this course.  
VPython, if used correctly, can be very helpful in learning new concepts in courses like physics, or helping to further study on models that may not be easy to create in real life.


==Downloading vPython==
In all cases you will need to have Python 2.7.9 installed. Future versions may also work, but be warned that it may cause VPython to behave erratically.


<!--{{spaces|2}}-->
[http://vpython.org/contents/download_windows.html For Windows]
==Downloading vPython==
 
Before learning how to code vPython, the first step is to download the proper application. If interested, before downloading vPython, glow script is a great resource to practice using vPython. Glow script also creates 3D models and run programs just like vPython, so it is a great resource to try out.
[http://vpython.org/contents/download_mac.html For Mac]


To download vPython, first either install Continuum Anaconda Python Distribution. Choose from either the Anaconda with Python 3.x  (this form is recommended on vypthon.org, especially if "Classic" VPython/Python 2.7 has previously been installed on the device.)
[http://vpython.org/contents/download_linux.html For Linux]


In order to access the necessary download, use this link: [https://www.python.org/downloads/]
Note for Linux: You can only install Classic VPython, which is no longer supported and may be missing some features and bug fixes that are present in the current version of VPython.


For windows, then go to the Power Shell or Command Prompt and type " pip install vpython ".
Alternatively, you can use GlowScript, a virtual environment that allows you to execute VPython code in your browser. You can create an account at [http://www.glowscript.org/ http://www.glowscript.org/].


For macs, go to Terminal and type " pip install vypython ".  
==Python Basics==
It's always helpful to have a background knowledge of Python, however basic, before proceeding with the applications more relevant to this course.


Vpython will then be successfully downloaded onto the device.  
    # Comments start with a number symbol. Use these liberally in order to keep track of the changes you make/the code you write.
    # We're always going to start our programs with the following headers to ensure that math works correctly.
    from__future__ import division
    from visual import*


    # Math works as you would expect.
    1 + 1  # -> 2
    2 - 1  # -> 1
    3 * 2  # -> 6
    8 / 4  # -> 4
    (1 + 3) * 2  # -> 8
    1 + (3 * 2)  # -> 7


<!--{{spaces|2}}-->
    # That is, until you need to do an exponent. But you shouldn't encounter anything much weirder than that math-wise.
    2 ** 3  # -> 8


==Mathematical Model==
    # However, these math operations are useless if we don't store the values anywhere.
Vpython can compute any equation, but some that may be most helpful and most useful for Physics can be found below. (Keep in mind you can alter these numbers to be whatever you need, these are just to provide an example):
    x = 1 + 1
    # Now if you try to access x in the future, it will have the value of '2'.


    # You can print your variables like this:
    print(x)
    # You can also add in some text with them like this:
    print("The value of x is ", x)


Always start vPython windows with:
    # Sometimes we only want to execute something based on a certain condition.
    if x == 2:
        y = 3
    # The '==' means that you're directly comparing two values. If they're equal, whatever is on the inside of the if-statement will be executed.
    # Now is a good time to note that whitespace is very important in Python. 'y = 3' will always execute if it isn't tabbed, so even if x is equal to 7, y will still become 3.
    # If you ever see me use whitespace in this tutorial, make sure you do as well.
    # Some other useful comparators: != (not equal), >, >= (greater than or equal to), <, <= (less than or equal to), 'and', 'or', 'not'
    # You can add onto the above if-statement by tacking on:
    elif x == 3:
        y = 4
    else:
        y = 5
    # With elif meaning "else if" for a second possible condition, and "else" for something that you want to execute if none of the earlier conditions are met.


from__future__ import division
    # You can also have a loop that executes code for a certain amount of time or based on a certain condition.
    while x < 5:
        print("x is ", x)
        x = x + 1
    # This will output the value of x up until it reaches 4.


from visual import*
Thus concludes our very, very brief foray into Python. That was simply the bare minimum required to understand what will be needed for this class. More concepts will be introduced as needed, whether that be in this tutorial or in a lab. For a more complete understanding of Python, you can look up other Python tutorials elsewhere on the Internet.


==Mathematical Model==
Vpython can compute any equation, but some that may be most helpful and most useful for Physics can be found below. (Keep in mind you can alter these numbers to be whatever you need, these are just to provide an example):


To update momentum:
To update momentum:


pf = pi + Fnet*deltat
    pf = pi + Fnet*deltat
 


To update position:
To update position:


objectf.pos = objecti.pos + (pcart/mcart)*deltat
    objectf.pos = objecti.pos + (pcart/mcart)*deltat
 


To create a vector:
To create a vector:


vector(0,0,0) -- fill in with whatever numbers the vector should be
    vector(0,0,0) -- fill in with whatever numbers the vector should be
 


Gravitational Force:
Gravitational Force:


CONSTANTS
    # Constants
 
    G = 6.7e-11
G = 6.7e-11
    mEarth = 6e24
 
    mcraft = 15e3
mEarth = 6e24
    deltat = 60
 
    t = 0
mcraft = 15e3
 
deltat = 60
 
t = 0
 


Finds the change in position:
Finds the change in position:


r=craft.pos-Earth.pos   
    r=craft.pos-Earth.pos   
 
    m=mcraft
m=mcraft
 


To find the magnitude of the change in position:
To find the magnitude of the change in position:


 
    rmag= mag(r)       
rmag= mag(r)       
 


To calculate the new magnitude of gravitational force:
To calculate the new magnitude of gravitational force:


 
    Fmag=(G*mcraft*mEarth)/(rmag**2)
Fmag=(G*mcraft*mEarth)/(rmag**2)
 


To calculate the direction of the change in position:
To calculate the direction of the change in position:


 
    rhat=r/rmag
rhat=r/rmag
 


To calculate net force:
To calculate net force:


Fnet=-Fmag*rhat
    Fnet=-Fmag*rhat
 
 


To calculate spring force:
To calculate spring force:


L0 = 0.3  
    L0 = 0.3  
 
    Lvec = ball.pos - ceiling.pos
Lvec = ball.pos - ceiling.pos
    Lhat = norm(Lvec)
 
    Lmag = mag(Lvec)
Lhat = norm(Lvec)
    Fspr = (-ks)*(Lmag - L0)*(Lhat)
 
Lmag = mag(Lvec)
 
Fspr = (-ks)*(Lmag - L0)*(Lhat)
 


To calculate kinetic energy:
To calculate kinetic energy:


Kinetic = (1/2)*(mball*(vel**2))
    Kinetic = (1/2)*(mball*(vel**2))
 


To create a graph:
To create a graph:


gdisplay(width=500, height=250, x=600, y=1)
    gdisplay(width=500, height=250, x=600, y=1)
 
    ygraph= gcurve(color=color.cyan)
ygraph= gcurve(color=color.cyan)
 
 


To add plots to the graph:
To add plots to the graph:


ygraph.plot(pos=(t, fnet.y))   
    ygraph.plot(pos=(t, fnet.y))   
 


==Computational Model==
==Computational Model==


VPython is used to create computational, 3D models of various real world situations in order to better visualize how different equations can manipulate different scenarios. This is very valuable since many of the equations and situations that are coded in vPython are extremely difficult to make a functioning model of in real life.  
VPython is used to create computational, 3D models of various real world situations in order to better visualize how different equations can manipulate different scenarios. This is very valuable since many of the equations and situations that are coded in vPython are extremely difficult to make a functioning model of in real life.  


For instance, the picture below is an example of program that was programmed to show the orbit of a craft around Earth.  
For instance, the picture below is an example of program that was programmed to show the orbit of a craft around Earth.  


[[File:Earthorbits.jpg]]
[[File:Earthorbits.jpg]]


This picture shows a graph that tracks.
This picture shows a graph that tracks.
[[File:PositionGraph.jpg]]
[[File:PositionGraph.jpg]]


==Examples==
==Examples==
Line 152: Line 153:
Sphere:
Sphere:


sphere= sphere(pos=vector(-4,-2,5), radius=.4, color=color.red)
    sphere= sphere(pos=vector(-4,-2,5), radius=.4, color=color.red)


Arrow:
Arrow:


bt=arrow(pos=sphere.pos, axis=sphere2.pos-sphere.pos, color=color.cyan)
    bt=arrow(pos=sphere.pos, axis=sphere2.pos-sphere.pos, color=color.cyan)


Vector:
Vector:


vector=vector(0, 0, 0)
    vector=vector(0, 0, 0)


Trail:
Trail:


trail = curve(color=sphere.color)
    trail = curve(color=sphere.color)
 
    trail.append(pos=sphere.pos)
trail.append(pos=sphere.pos)


Setting Scene Range:
Setting Scene Range:


scene.range=11*sphere.radius
    scene.range=11*sphere.radius
 


Helix:
Helix:


spring = helix(pos=ceiling.pos, color=color.cyan, thickness=.003, coils=40, radius=0.015)  
    spring = helix(pos=ceiling.pos, color=color.cyan, thickness=.003, coils=40, radius=0.015)  


Intermediate:
Intermediate:
Line 183: Line 182:
Setup graphing windows:
Setup graphing windows:


gdisplay(width=500, height=250, x=600, y=1)
    gdisplay(width=500, height=250, x=600, y=1)
 
    ygraph = gcurve(color=color.yellow)
ygraph = gcurve(color=color.yellow)
    gdisplay(width=500, height=250, x=600, y=300)
 
gdisplay(width=500, height=250, x=600, y=300)


Plotting:
Plotting:


pgraph = gcurve(color=color.blue)
    pgraph = gcurve(color=color.blue)
 
    ygraph.plot(pos=(time, Fnet.y))
ygraph.plot(pos=(time, Fnet.y))
    pgraph.plot(pos=(time, sphere.y))
 
pgraph.plot(pos=(time, sphere.y))
 


Difficult:
Difficult:
Line 202: Line 196:
Using Loops to update Equations:
Using Loops to update Equations:


 
Constants:
CONSTANTS:


G = ?
G = ?
Line 217: Line 210:
t = ?
t = ?


Objects and initial values:


OBJECTS AND INITIAL VALUES:
    Earth = sphere(pos=vector(0,0,0), radius=6.4e6, color=color.cyan)
 
    scene.range=11*Earth.radius
Earth = sphere(pos=vector(0,0,0), radius=6.4e6, color=color.cyan)
    Moon = sphere(pos=(4e8, 0, 0), radius=1.75e6, color=color.white)
 
scene.range=11*Earth.radius
 
Moon = sphere(pos=(4e8, 0, 0), radius=1.75e6, color=color.white)


Add a radius for the spacecraft. It should be BIG, so it can be seen:
Add a radius for the spacecraft. It should be BIG, so it can be seen:


craft = sphere(pos=vector(-6.656e7,-3.648e6,0), radius= 10000, color=color.yellow)
    craft = sphere(pos=vector(-6.656e7,-3.648e6,0), radius= 10000, color=color.yellow)
vcraft = vector(206, 2645,0)
    vcraft = vector(206, 2645,0)
pcraft = mcraft*vcraft
    pcraft = mcraft*vcraft
pArrow=arrow(color=color.green)
    pArrow=arrow(color=color.green)
fArrow=arrow(color=color.cyan)
    fArrow=arrow(color=color.cyan)
dpArrow=arrow(color=color.red)
    dpArrow=arrow(color=color.red)
Fnet_tangent_arrow = arrow(color=color.yellow)
    Fnet_tangent_arrow = arrow(color=color.yellow)
Fnet_perp_arrow= arrow(color=color.magenta)
    Fnet_perp_arrow= arrow(color=color.magenta)


This creates a trail for the spacecraft:
This creates a trail for the spacecraft:


trail = curve(color=craft.color)   
    trail = curve(color=craft.color)   


And this prevents zooming in or out:
And this prevents zooming in or out:
    
    
scene.autoscale = 0                 
    scene.autoscale = 0                 
pscale=Earth.radius/mag(pcraft)
    pscale=Earth.radius/mag(pcraft)
fscale=Earth.radius/((G*mEarth*mcraft)*mag(craft.pos-Earth.pos)**2)
    fscale=Earth.radius/((G*mEarth*mcraft)*mag(craft.pos-Earth.pos)**2)
dpscale=500*Earth.radius/mag(pcraft)
    dpscale=500*Earth.radius/mag(pcraft)
print("p=", pcraft)
    print("p=", pcraft)


CALCULATIONS:
Calculations:


Sets time for loop to run:
Sets time for loop to run:


while t < 165240:  
    while t < 165240:  
 
This slows down the animation (runs faster with bigger number):
This slows down the animation (runs faster with bigger number):
     rate(10000)   
     rate(10000)   


    Add statements here for the iterative update of gravitational
Add statements here for the iterative update of gravitational
    force, momentum, and position.
force, momentum, and position.


     r = craft.pos-Earth.pos
     r = craft.pos-Earth.pos
     rmag = sqrt(r.x**(2)+r.y**(2)+r.z**(2))
     rmag = sqrt(r.x**(2)+r.y**(2)+r.z**(2))
Line 295: Line 286:
     scene.range=craft.radius*600
     scene.range=craft.radius*600
      
      
   Uncomment these two lines to exit the loop if
   Uncomment these two lines to exit the loop if
   the spacecraft crashes onto the Earth.
   the spacecraft crashes onto the Earth.
Line 305: Line 294:
     trail.append(pos=craft.pos)   
     trail.append(pos=craft.pos)   
     t = t+deltat
     t = t+deltat
==Connectedness==
vPython codes are very useful in modeling situations that may not be easy to construct models of in real life. The ability to map out a real life scenario in code form and then be able to tweak that code and see how the situation changes is priceless to scientists and students alike. Being able to have a visual on VPython for something that may not be able to be easily modeled in real life is what helps make VPython so valuable. In relation to the field of Industrial Engineering, VPython could be useful in modeling different systems and seeing which conditions promote the most optimal results. The computer simulations that VPython produces can assist in production and end up saving companies time and money. In addition, Industrial Engineers use a lot of Python and so their background knowledge of Python makes VPython much more accessible to them.
==History==
A cT language was created in 1997 and was based a language of the PLATO computer-based education system. In 2000 Ruth Chabay, David Scherer, and Bruce Sherwood develop VPython. This form of VPython would be later referred to as "Classic" VPython. From 2002 to 2006 an engineering student named Jonathan Brandmeyer helped make important contributions to VPython 3. As the years went on more and more changes were made in order to make VPython what it is today.
==Extra Resources==
If having trouble while trying to use VPython it made be helpful to watch someone else code using it first. While I do not own any of the following videos, they may be helpful resources to watch in order to become more proficient in VPython.
[https://www.youtube.com/watch?v=KbOyKOlWBrs]
[https://www.youtube.com/watch?v=jLHS0ZvYE5Y]
==References==
[http://vpython.org/contents/history.html]
[https://wiki.python.org/moin/VPython]
[http://vpython.org/contents/experienced.html]
[http://vpython.org/contents/announcements/get-vpython.html]
[https://matterandinteractions.wordpress.com/2016/04/27/a-time-line-for-vpython-development/]

Revision as of 15:49, 1 November 2017

Edited by Zach Sanchez - Fall 2017 (in progress)

The Main Idea

VPython is an extension of the Python programming language that contains a 3D graphics module called Visual, which allows users to create simple simulations of physics problems. Its primary use is for educational purposes, although it has been used in research before in the past. We will use VPython on occasion to aid us in visualizing and experimenting with the ideas that we learn in this course.

Downloading vPython

In all cases you will need to have Python 2.7.9 installed. Future versions may also work, but be warned that it may cause VPython to behave erratically.

For Windows

For Mac

For Linux

Note for Linux: You can only install Classic VPython, which is no longer supported and may be missing some features and bug fixes that are present in the current version of VPython.

Alternatively, you can use GlowScript, a virtual environment that allows you to execute VPython code in your browser. You can create an account at http://www.glowscript.org/.

Python Basics

It's always helpful to have a background knowledge of Python, however basic, before proceeding with the applications more relevant to this course.

   # Comments start with a number symbol. Use these liberally in order to keep track of the changes you make/the code you write.
   # We're always going to start our programs with the following headers to ensure that math works correctly.
   from__future__ import division
   from visual import*
   # Math works as you would expect.
   1 + 1  # -> 2
   2 - 1  # -> 1
   3 * 2  # -> 6
   8 / 4  # -> 4
   (1 + 3) * 2  # -> 8
   1 + (3 * 2)  # -> 7
   # That is, until you need to do an exponent. But you shouldn't encounter anything much weirder than that math-wise.
   2 ** 3  # -> 8
   # However, these math operations are useless if we don't store the values anywhere.
   x = 1 + 1
   # Now if you try to access x in the future, it will have the value of '2'.
   # You can print your variables like this:
   print(x)
   # You can also add in some text with them like this:
   print("The value of x is ", x)
   # Sometimes we only want to execute something based on a certain condition.
   if x == 2:
       y = 3
   # The '==' means that you're directly comparing two values. If they're equal, whatever is on the inside of the if-statement will be executed.
   # Now is a good time to note that whitespace is very important in Python. 'y = 3' will always execute if it isn't tabbed, so even if x is equal to 7, y will still become 3.
   # If you ever see me use whitespace in this tutorial, make sure you do as well.
   # Some other useful comparators: != (not equal), >, >= (greater than or equal to), <, <= (less than or equal to), 'and', 'or', 'not'
   # You can add onto the above if-statement by tacking on:
   elif x == 3:
       y = 4
   else:
       y = 5
   # With elif meaning "else if" for a second possible condition, and "else" for something that you want to execute if none of the earlier conditions are met.
   # You can also have a loop that executes code for a certain amount of time or based on a certain condition.
   while x < 5:
       print("x is ", x)
       x = x + 1
   # This will output the value of x up until it reaches 4.

Thus concludes our very, very brief foray into Python. That was simply the bare minimum required to understand what will be needed for this class. More concepts will be introduced as needed, whether that be in this tutorial or in a lab. For a more complete understanding of Python, you can look up other Python tutorials elsewhere on the Internet.

Mathematical Model

Vpython can compute any equation, but some that may be most helpful and most useful for Physics can be found below. (Keep in mind you can alter these numbers to be whatever you need, these are just to provide an example):

To update momentum:

   pf = pi + Fnet*deltat

To update position:

   objectf.pos = objecti.pos + (pcart/mcart)*deltat

To create a vector:

   vector(0,0,0) -- fill in with whatever numbers the vector should be

Gravitational Force:

   # Constants
   G = 6.7e-11
   mEarth = 6e24
   mcraft = 15e3
   deltat = 60
   t = 0

Finds the change in position:

   r=craft.pos-Earth.pos  
   m=mcraft

To find the magnitude of the change in position:

   rmag= mag(r)      

To calculate the new magnitude of gravitational force:

   Fmag=(G*mcraft*mEarth)/(rmag**2)

To calculate the direction of the change in position:

   rhat=r/rmag

To calculate net force:

   Fnet=-Fmag*rhat

To calculate spring force:

   L0 = 0.3 
   Lvec = ball.pos - ceiling.pos
   Lhat = norm(Lvec)
   Lmag = mag(Lvec)
   Fspr = (-ks)*(Lmag - L0)*(Lhat)

To calculate kinetic energy:

   Kinetic = (1/2)*(mball*(vel**2))

To create a graph:

   gdisplay(width=500, height=250, x=600, y=1)
   ygraph= gcurve(color=color.cyan)

To add plots to the graph:

   ygraph.plot(pos=(t, fnet.y))  

Computational Model

VPython is used to create computational, 3D models of various real world situations in order to better visualize how different equations can manipulate different scenarios. This is very valuable since many of the equations and situations that are coded in vPython are extremely difficult to make a functioning model of in real life.

For instance, the picture below is an example of program that was programmed to show the orbit of a craft around Earth.

This picture shows a graph that tracks.

Examples

Simple:

Creating Shapes:

Sphere:

   sphere= sphere(pos=vector(-4,-2,5), radius=.4, color=color.red)

Arrow:

   bt=arrow(pos=sphere.pos, axis=sphere2.pos-sphere.pos, color=color.cyan)

Vector:

   vector=vector(0, 0, 0)

Trail:

   trail = curve(color=sphere.color)
   trail.append(pos=sphere.pos)

Setting Scene Range:

   scene.range=11*sphere.radius

Helix:

   spring = helix(pos=ceiling.pos, color=color.cyan, thickness=.003, coils=40, radius=0.015) 

Intermediate:

Graphs:

Setup graphing windows:

   gdisplay(width=500, height=250, x=600, y=1)
   ygraph = gcurve(color=color.yellow)
   gdisplay(width=500, height=250, x=600, y=300)

Plotting:

   pgraph = gcurve(color=color.blue)
   ygraph.plot(pos=(time, Fnet.y))
   pgraph.plot(pos=(time, sphere.y))

Difficult:

Using Loops to update Equations:

Constants:

G = ?

mEarth = ?

mmoon = ?

mcraft = ?

deltat = ?

t = ?

Objects and initial values:

   Earth = sphere(pos=vector(0,0,0), radius=6.4e6, color=color.cyan)
   scene.range=11*Earth.radius
   Moon = sphere(pos=(4e8, 0, 0), radius=1.75e6, color=color.white)

Add a radius for the spacecraft. It should be BIG, so it can be seen:

   craft = sphere(pos=vector(-6.656e7,-3.648e6,0), radius= 10000, color=color.yellow)
   vcraft = vector(206, 2645,0)
   pcraft = mcraft*vcraft
   pArrow=arrow(color=color.green)
   fArrow=arrow(color=color.cyan)
   dpArrow=arrow(color=color.red)
   Fnet_tangent_arrow = arrow(color=color.yellow)
   Fnet_perp_arrow= arrow(color=color.magenta)

This creates a trail for the spacecraft:

   trail = curve(color=craft.color)  

And this prevents zooming in or out:

   scene.autoscale = 0                 
   pscale=Earth.radius/mag(pcraft)
   fscale=Earth.radius/((G*mEarth*mcraft)*mag(craft.pos-Earth.pos)**2)
   dpscale=500*Earth.radius/mag(pcraft)
   print("p=", pcraft)

Calculations:

Sets time for loop to run:

   while t < 165240: 

This slows down the animation (runs faster with bigger number):

   rate(10000)   

Add statements here for the iterative update of gravitational force, momentum, and position.

   r = craft.pos-Earth.pos
   rmag = sqrt(r.x**(2)+r.y**(2)+r.z**(2))
   Fmag= G*mEarth*mcraft/(rmag**2)
   rhat= r/rmag
   rmoon= craft.pos - Moon.pos
   rmoonmag= mag(rmoon)
   rmoonhat= norm(rmoon)
   Fmoonmag= G*mmoon*mcraft/(rmoonmag**2)
   Fmoon= -Fmoonmag*rmoonhat
   p_init= mag(pcraft)
   pcraft_i=pcraft+vector(0,0,0)
   Fearth= -Fmag*rhat
   Fnet= Fearth + Fmoon
   pcraft=Fnet*deltat+pcraft
   p_final=mag(pcraft)
   Fnet_tangent = (p_final-p_init)*norm(pcraft)/deltat
   Fnet_tangent_arrow.pos=craft.pos
   Fnet_tangent_arrow.axis=Fnet_tangent*fscale
   Fnet_perp = Fnet-Fnet_tangent
   Fnet_perp_arrow.pos=craft.pos
   Fnet_perp_arrow.axis=Fnet_perp*fscale
   vcraft=pcraft/mcraft
   craft.pos=vcraft*deltat+craft.pos
   pArrow.pos=craft.pos
   pArrow.axis=pcraft*pscale
   fArrow.pos=craft.pos
   fArrow.axis=Fnet*fscale
   deltap= pcraft-pcraft_i
   dpArrow.pos=craft.pos
   dpArrow.axis=deltap*dpscale
   scene.center=craft.pos
   scene.range=craft.radius*600
   
  Uncomment these two lines to exit the loop if
  the spacecraft crashes onto the Earth.
   if rmag < Earth.radius: 
       break
   trail.append(pos=craft.pos)  
   t = t+deltat