Re: [Visualpython-users] strange math

[Steve S. <st...@sp...>]

Hi Lenore,

It's about python assignments. You are assigning the *same*  
acceleration vector to both objects, then changing the y component of  
the same vector.

Instead of assigning both accelerations to the same vector (gravity)  
try initializing them with different vectors:

pixie.acceleration = vector(0,-9.8,0)
air.acceleration = vector(0,-9.8,0)

then when you fiddle with the y components, it will be the y  
components of different vector objects.

That should work!
-steve

On Sep 12, 2009, at 7:26 AM, Lenore Horner wrote:

> Sorry.  I was in too big a hurry and forgot to paste the code.  Here
> it is.  I've put arrows off to the right indicating the lines where
> both air.acceleration and pixie.acceleration are being changed despite
> the fact that only air.acceleration appears in the code.  I've
> included all of the while loop.  I don't see anywhere that I'm
> reassigning pixie.acceleration from its original value of gravity but
> it changes as soon as it hits those to statements (and not before).
>
> Thanks,
> Lenore
>
>
> angle = math.pi/4
> speed = 13.0
>
> power = 2
> constant = 1
>
> gravity = vector(0,-9.8,0)
>
> launch_velocity = vector(speed*math.cos(angle),speed*math.sin 
> (angle),0)
>
> pixie = sphere(pos=vector(-9,-3.55,0), radius=0.2, color=color.red)
> pixie.velocity = launch_velocity
> pixie.acceleration = gravity
>
> air = sphere(pos=vector(-9,-3.55,0.3), radius=0.15, color=color.blue)
> air.velocity = launch_velocity
> air.acceleration = gravity
>
> scene.mouse.getclick()    # Don't launch until we're watching
>
> dt = 0.01
> while 1:
>      rate(100)
>      air.pos = air.pos + air.velocity*dt
>      if air.y < -3.55:
>          air.velocity = vector(0,0,0)
>      else:
>          air.velocity = air.velocity + air.acceleration*dt
>          air.acceleration.y = gravity.y - sign(air.velocity.y) *
> constant * air.radius * air.velocity.y**power    <-----
>          print  "5", air.acceleration, pixie.acceleration
>          air.acceleration.x = -sign(air.velocity.x) * constant *
> air.radius * air.velocity.x**power              <-------
>          print "6", air.acceleration, pixie.acceleration
>
>      pixie.pos = pixie.pos + pixie.velocity*dt
>      if pixie.y < -3.55:
>          pixie.velocity = vector(0,0,0)
>      else:
>          pixie.velocity = pixie.velocity + pixie.acceleration*dt
>
>
> On Sep 11, 2009, at 18:20 , Bruce Sherwood wrote:
>
>> Can you explain the context of your question? I have no idea what
>> program or
>> documentation you're referring to.
>>
>> Bruce Sherwood
>>
>> Lenore Horner wrote:
>>> Perhaps I'm just blind, but I can't figure out why the assignment
>>> statements above print "5" and print "6" affect both acceleration
>>> vectors, but they do.  How do I change the acceleration vector of  
>>> one
>>> object without touching the vector of other objects?
>>>
>>> Thanks,
>>> Lenore
>>
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