5.7.1. Exercise: Statistics

We recorded this series of forces using a gait force platform, where the first axis corresponds to time and the second axis corresponds to \(F_x\), \(F_y\) and \(F_z\).

import numpy as np

forces = np.array(
    [
        [0.17619048, 0.82380952, 17.61904762],
        [0.21428571, 0.78571429, 21.42857143],
        [0.17619048, 0.82380952, 17.61904762],
        [0.17619048, 0.82380952, 17.61904762],
        [0.17619048, 0.82380952, 17.61904762],
        [0.32857143, 0.67142857, 32.85714286],
        [0.25238095, 0.74761905, 25.23809524],
        [0.17619048, 0.82380952, 17.61904762],
        [0.29047619, 0.70952381, 29.04761905],
        [0.32857143, 0.67142857, 32.85714286],
        [0.25238095, 0.74761905, 25.23809524],
        [0.21428571, 0.78571429, 21.42857143],
        [0.67142857, 0.32857143, 67.14285714],
        [8.1, -7.1, 810.0],
        [8.70952381, -7.70952381, 870.95238095],
        [8.02380952, -7.02380952, 802.38095238],
        [7.26190476, -6.26190476, 726.19047619],
        [7.75714286, -6.75714286, 775.71428571],
        [9.47142857, -8.47142857, 947.14285714],
        [9.85238095, -8.85238095, 985.23809524],
        [9.54761905, -8.54761905, 954.76190476],
        [8.63333333, -7.63333333, 863.33333333],
        [7.83333333, -6.83333333, 783.33333333],
        [6.76666667, -5.76666667, 676.66666667],
        [5.2047619, -4.2047619, 520.47619048],
        [2.95714286, -1.95714286, 295.71428571],
        [1.50952381, -0.50952381, 150.95238095],
        [0.48095238, 0.51904762, 48.0952381],
        [-0.01428571, 1.01428571, -1.42857143],
        [0.02380952, 0.97619048, 2.38095238],
        [0.17619048, 0.82380952, 17.61904762],
        [0.02380952, 0.97619048, 2.38095238],
        [0.06190476, 0.93809524, 6.19047619],
        [0.06190476, 0.93809524, 6.19047619],
        [0.06190476, 0.93809524, 6.19047619],
        [0.02380952, 0.97619048, 2.38095238],
        [0.06190476, 0.93809524, 6.19047619],
        [0.13809524, 0.86190476, 13.80952381],
    ]
)

1. Write one code line that calculates the three mean forces \(\overline{F_x}\), \(\overline{F_y}\) and \(\overline{F_z}\) as a unidimensional array of length 3.

2. Write one code line that calculates the series of resulting force (\(F_\text{tot} = \sqrt{F_x^2 + F_y^2 + F_z^2}\)).

3. Write one code line that calculates the mean resulting force \(\overline{F_\text{tot}}\) as a float.

Show code cell content Hide code cell content

# 1.
print("== 1 ==")
print(
    np.mean(forces, axis=0),
)

# 2.
print("== 2 ==")
print(
    np.sqrt(np.sum(forces**2, axis=1)),
)

# 3.
print("== 3 ==")
print(
    np.mean(np.sqrt(np.sum(forces**2, axis=1)), axis=0),
)

== 1 ==
[  2.79373434  -1.79373434 279.37343358]
== 2 ==
[ 17.6391764   21.44404204  17.6391764   17.6391764   17.6391764
  32.86564487  25.25042736  17.6391764   29.05773517  32.86564487
  25.25042736  21.44404204  67.14701811 810.07161412 871.03004681
 802.45181049 726.253781   775.78249871 947.22809549 985.32712252
 954.84790077 863.41024239 783.40230192 676.72506973 520.51919698
 295.7355472  150.96078826  48.10044338   1.75208331   2.57341193
  17.6391764    2.57341193   6.26145753   6.26145753   6.26145753
   2.57341193   6.26145753  13.83708416]
== 3 ==
279.50951929881217