Using numpy take the inputs and return points that cross the x-axis-CodePudding

I got this question. Write a function cos_x_crossings(begin, end, skip), where the input parameters are entered and returns x-points as a list that crosses the x-axis.(x-value that just before it crosses) I am not allowed to use for or while loop. Required to use NumPy.

test 1

import math
ans = cos_x_crossings(0, 4 * math.pi, 0.01)
for val in ans:
    print(round(val, 2))

result 1

test 2

import math
ans = cos_x_crossings(0, 2 * math.pi, 0.1)
for val in ans:
    print(round(val, 2))

result 2

1.5
4.7

CodePudding user response：

Since we already know that cos(x) is zero if and only x is of the form pi/2 k pi, all you have to do is call numpy.arange with the correct parameters to generate the output array.

import numpy as np

def cos_x_crossings(xstart, xstop, xstep):
  ystart = (np.trunc((xstart - np.pi/2) / np.pi)   0.5) * np.pi
  ystop = xstop
  ystep = np.pi
  return (np.arange(ystart, ystop, ystep) // xstep) * xstep

print( cos_x_crossings(0, 4 * np.pi, 0.01) )
# [ 1.57  4.71  7.85 10.99]

print( cos_x_crossings(0, 2 * np.pi, 0.1) )
# [1.5 4.7]