CODEWITHSUNDEEP
pythonnumpyphysicsshapes
PARCB
PARCB

Reputation: 61

Meaning of the return of np.shape()

I have a program in numpy utf8, which allows me to calculate the coordinates of a parabolic shot from the ground. I need to create a function which returns the coordinates (#1), create the different arrays of values to work with (#2), and finally use the function to generate the different coordinates for each pack of values

#1
def coordenadas(v,a,t,g=9.81):
    rad=deg2rad(a)
    x=v*cos(a)*t
    y=v*sin(a)*t-(1./2.)*g*(t**2)
    xy=array([x,y]).T
    return xy
#2
v=arange(50,100,10) #m/s
adegree=arange(45,90,5) #degrees
a=deg2rad(adegree) #rads
t=linspace(0,10,50) #segundos
#3
v.shape=(5,1,1)
a.shape=(1,9,1)
t.shape=(1,1,50)
#5
XY=coordenadas(v,a,t,g=9.81)
print shape(XY)
print XY
#4

My question is that shape(XY) returns

(50L, 9L, 5L, 2L)

And XY (only a bit, is too long)

[[[[   0.            0.        ]
   [   0.            0.        ]
   [   0.            0.        ]
   [   0.            0.        ]
   [   0.            0.        ]]

And more boxes of this shape

What this really means(big boxes, boxes, small boxes, rows, columns) ???

Upvotes: 0

Views: 2973

Answers (2)

Dschoni
Dschoni

Reputation: 3872

Numpy arrays are basically matrices, where each box [] represents the start of a new dimension. As an easy example the matrix

11
23

could be written in numpy as:

a = numpy.array([[1,1],[2,3]])

which then would be printed as

array([[1, 1],
       [2, 3]])

As this is a two-dimensional matrix, the outer "box" marks the edges of the matrix, whereas the inner boxes are the rows of the matrix with the , separating the entries. Calling a.shape without an argument gives the shape of the 2x2 matrix:

(2, 2)

Calling the shape method with argument reshapes the matrix given to the shape defined in the argument. But to further help you with the code:

1

Your function definition seems to be totally fine, except I don't see a reason, why you export x and y in an array, rather than just returning two different values.

2

The initialization of your arrays seem to be fine as well.

3

There is totally no reason to reshape the arrays you just created, just leave them as they are.

4

You have to call the function separately with each set of values to create the coordinates. Do that by using an itteration over the arrays you just created.

Upvotes: 0

valentin
valentin

Reputation: 3608

(50L, 9L, 5L, 2L) means a 4D array.

You can visualize as a 50x9 matrix and each cell of this matrix contains a 5x2 matrix

Upvotes: 2

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