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So I need to write code that accomplishes the following:

Write a Python code that produces a variable op_table that is a numpy array with three axes, i, j, and k. Define three arrays:

xi ranges from 0 (included) to 9 (included) in steps of 1,

yj ranges form 10 (included) to 11 (included) in 20 equal-size steps,

zk ranges form 10 to 106 in five steps (i.e. with six entries total), where zk=10zk−1.

Then create the final array op_table that satisfies:

op_table[i,j,k]=sin(xi)⋅yj+zk

My question lies in how to initially set the values. I've only seen numpy arrays created in manners such as np.array([1,2,3,4]) or np.arrange(10). Also, how is this set-up? Is the first column the x-axis, second the y-axis and so forth?

    import numpy as np
    import math

    xi = np.linspace(0,9, num=10)
    yj = np.linspace(10,11,20, endpoint=True)
    zk = [10, 10**2, 10**3, 10**4, 10**5, 10**6]


   op_table = np.random.rand(10,20,6)
   for i in range (0,10):
      for j in range (0,20):
         for k in range (0,6):
             op_table[i,j,k] = math.sin(xi[i]) * yj[j] + zk[k]
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1 Answer 1

up vote 0 down vote

Don't personally believe in spoon-feeding answers, but it looks like you've misinterpreted the problem. The problem doesn't actually require that you generate any matrix, except by solving the second equation. Numpy happens to have a very helpful function called linspace that does almost exactly this.

import numpy as np

xi = np.linspace(0, 10)
yj = np.linspace(10, 11, 20)

Other than that, this seems to be a math problem, and this should get you 80% of the way to a solution. If you need help with the math, there's another stackexchange for that.

More np.linspace docs: http://docs.scipy.org/doc/numpy/reference/generated/numpy.linspace.html Math stackexchange: http://math.stackexchange.com/

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Wasn't looking for the answer - just a hint in the right direction on how to assign to the arrays. Thanks for the help! –  user3424684 Sep 3 at 1:13
    
So I implemented what I think works, but it says the array has the wrong shape (10,20,6), but wouldn't that be correct based off what is given? Here is what I did (edited above) –  user3424684 Sep 3 at 2:10
    
@user3424684 It's hard for me to say. The problem as detailed above is a little non-sensical in terms of pure math (zk specifically is definitely not correct as written). You should probably also not use any for loops if you've got a numpy array (it kind of defeats the purpose.) –  Slater Tyranus Sep 3 at 2:27
    
Got it. I'll try using newaxis then. But what's wrong with zk? Don't you just start at 10 and keep multiplying by 10 at each additional term until 10^6? –  user3424684 Sep 3 at 2:50
    
Nevermind, I got it. Since it said 20 equal steps in yj, that implies 21 entries, so the shape was wrong. Thanks again for the help –  user3424684 Sep 3 at 2:55

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