bug when adding non-normalized transfer functions

[twmacro]

Hi!

Adding (110 s) / (85 s^2 + 20 s + 1) and 0.25 gives an incorrect result, but it works fine if the first transfer function is normalized. Here is a little example ... it shows that the numerator never gets divided by 85:

import numpy as np
import harold


num = np.array([110.0, 0.0])
den = np.array([85.0, 20.0, 1.0])

h_a = harold.Transfer(num, den)
h_b = harold.Transfer(num / 85.0, den / 85.0)

h2 = harold.Transfer(0.25, 1.0)

h_sum_a = h_a + h2
h_sum_b = h_b + h2
print(f"h_sum_a.num = {h_sum_a.num}")
print(f"h_sum_a.den = {h_sum_a.den}")

print()
print(f"h_sum_b.num = {h_sum_b.num}")
print(f"h_sum_b.den = {h_sum_b.den}")

The output is:

h_sum_a.num = [[2.50000000e-01 1.10058824e+02 2.94117647e-03]]
h_sum_a.den = [[1.         0.23529412 0.01176471]]

h_sum_b.num = [[0.25       1.35294118 0.00294118]]
h_sum_b.den = [[1.         0.23529412 0.01176471]]

[ilayn]

Hi @twmacro Thank you for taking the time to report this. I am a bit disappointed that I didn't test this. I'll fix this and add some more tests hopefully today and push it.

[twmacro]

Hi @ilayn, that's awesome! I really appreciate your quick turn-around. I'm making good use of harold! :-)

[ilayn]

Now it should be a bit more intuitive to add these things 😃 Note that, you can directly add scalars

import numpy as np
import harold


num = np.array([110.0, 0.0])
den = np.array([85.0, 20.0, 1.0])

h_a = harold.Transfer(num, den)
h_b = harold.Transfer(num / 85.0, den / 85.0)
h1 = h_a + 0.25
h2 = h_b + 0.25
print(f'Unscaled num: {h1.num}\nUnscaled den: {h1.den}')
print(f'scaled num:   {h2.num}\nscaled den:   {h2.den}')
print(f'Minimal realization: {harold.minimal_realization(h1).polynomials}')

This gives

Unscaled num: [[ 21.25 115.     0.25]]
Unscaled den: [[85. 20.  1.]]
scaled num:   [[0.25       1.35294118 0.00294118]]
scaled den:   [[1.         0.23529412 0.01176471]]
Minimal realization: (array([[0.25      , 1.35294118, 0.00294118]]), array([[1.        , 0.23529412, 0.01176471]]))

[twmacro]

Fantastic, @ilayn! And many thanks for the usage tips -- I will make good use of them! 😃