-
galois.FieldArray.log(base: ElementLike | ArrayLike | None =
None
) int | ndarray Computes the discrete logarithm of the array \(x\) base \(\beta\).
- Parameters:¶
- base: ElementLike | ArrayLike | None =
None
¶ A primitive element or elements \(\beta\) of the finite field that is the base of the logarithm. The default is
None
which usesprimitive_element
.Slower performance
If the
FieldArray
is configured to use lookup tables (ufunc_mode == "jit-lookup"
) and this method is invoked with a base different fromprimitive_element
, then explicit calculation will be used (which is slower than using lookup tables).
- base: ElementLike | ArrayLike | None =
- Returns:¶
An integer array \(i\) of powers of \(\beta\) such that \(\beta^i = x\). The return array shape obeys NumPy broadcasting rules.
Examples
Compute the logarithm of \(x\) with default base \(\alpha\), which is the specified primitive element of the field.
In [1]: GF = galois.GF(3**5) In [2]: alpha = GF.primitive_element; alpha Out[2]: GF(3, order=3^5) In [3]: x = GF.Random(10, low=1); x Out[3]: GF([136, 239, 224, 6, 134, 71, 109, 41, 96, 148], order=3^5) In [4]: i = x.log(); i Out[4]: array([ 99, 162, 155, 122, 42, 182, 165, 216, 50, 54]) In [5]: np.array_equal(alpha ** i, x) Out[5]: True
In [6]: GF = galois.GF(3**5, repr="poly") In [7]: alpha = GF.primitive_element; alpha Out[7]: GF(α, order=3^5) In [8]: x = GF.Random(10, low=1); x Out[8]: GF([ α^2 + 2α + 2, α^3 + 2α + 1, α^4 + α^3 + 2α^2, 2α^4 + α^3 + 2α^2, 2α^4 + α^3 + α^2 + 2, α^4 + 2α^2 + 2α + 2, α^4 + 2α^3 + α^2 + 1, 2α^4 + α^3 + 2α^2 + 2α, 2α^3 + 2α + 2, α^3], order=3^5) In [9]: i = x.log(); i Out[9]: array([222, 198, 211, 19, 33, 105, 179, 183, 93, 3]) In [10]: np.array_equal(alpha ** i, x) Out[10]: True
In [11]: GF = galois.GF(3**5, repr="power") In [12]: alpha = GF.primitive_element; alpha Out[12]: GF(α, order=3^5) In [13]: x = GF.Random(10, low=1); x Out[13]: GF([ α^79, α^123, α^56, α^194, α^219, α^212, α^194, α^184, α^84, α^132], order=3^5) In [14]: i = x.log(); i Out[14]: array([ 79, 123, 56, 194, 219, 212, 194, 184, 84, 132]) In [15]: np.array_equal(alpha ** i, x) Out[15]: True
With the default argument,
numpy.log()
andlog()
are equivalent.In [16]: np.array_equal(np.log(x), x.log()) Out[16]: True
Compute the logarithm of \(x\) with a different base \(\beta\), which is another primitive element of the field.
In [17]: beta = GF.primitive_elements[-1]; beta Out[17]: GF(242, order=3^5) In [18]: i = x.log(beta); i Out[18]: array([109, 87, 16, 90, 149, 26, 90, 18, 24, 176]) In [19]: np.array_equal(beta ** i, x) Out[19]: True
In [20]: beta = GF.primitive_elements[-1]; beta Out[20]: GF(2α^4 + 2α^3 + 2α^2 + 2α + 2, order=3^5) In [21]: i = x.log(beta); i Out[21]: array([109, 87, 16, 90, 149, 26, 90, 18, 24, 176]) In [22]: np.array_equal(beta ** i, x) Out[22]: True
In [23]: beta = GF.primitive_elements[-1]; beta Out[23]: GF(α^185, order=3^5) In [24]: i = x.log(beta); i Out[24]: array([109, 87, 16, 90, 149, 26, 90, 18, 24, 176]) In [25]: np.array_equal(beta ** i, x) Out[25]: True
Compute the logarithm of a single finite field element base all of the primitive elements of the field.
In [26]: x = GF.Random(low=1); x Out[26]: GF(192, order=3^5) In [27]: bases = GF.primitive_elements In [28]: i = x.log(bases); i Out[28]: array([158, 104, 80, 200, 182, 156, 228, 222, 52, 144, 40, 214, 196, 188, 60, 102, 86, 118, 234, 54, 14, 230, 76, 74, 98, 170, 2, 124, 38, 90, 184, 128, 48, 94, 208, 134, 4, 32, 30, 174, 36, 46, 204, 92, 168, 12, 96, 42, 68, 206, 142, 226, 116, 62, 112, 16, 130, 136, 192, 56, 122, 82, 172, 24, 150, 178, 10, 58, 100, 84, 146, 224, 152, 216, 18, 78, 164, 202, 210, 236, 212, 8, 238, 50, 34, 20, 148, 166, 160, 126, 72, 138, 108, 186, 194, 106, 140, 120, 190, 6, 26, 70, 240, 232, 64, 180, 114, 28, 162, 218]) In [29]: np.all(bases ** i == x) Out[29]: True
In [30]: x = GF.Random(low=1); x Out[30]: GF(2α^3 + α^2 + 2α, order=3^5) In [31]: bases = GF.primitive_elements In [32]: i = x.log(bases); i Out[32]: array([ 18, 116, 52, 130, 82, 174, 124, 108, 58, 142, 26, 6, 200, 98, 160, 30, 68, 234, 140, 144, 118, 210, 122, 36, 100, 50, 86, 8, 182, 240, 168, 180, 128, 170, 232, 196, 172, 166, 80, 222, 96, 42, 60, 84, 206, 32, 14, 112, 20, 146, 56, 38, 148, 4, 218, 204, 24, 40, 28, 230, 164, 138, 136, 64, 158, 152, 188, 74, 186, 224, 228, 194, 2, 92, 48, 208, 34, 216, 76, 226, 162, 102, 70, 214, 10, 134, 72, 120, 104, 94, 192, 126, 46, 12, 114, 202, 212, 78, 184, 16, 150, 106, 156, 54, 90, 238, 62, 236, 190, 178]) In [33]: np.all(bases ** i == x) Out[33]: True
In [34]: x = GF.Random(low=1); x Out[34]: GF(α^104, order=3^5) In [35]: bases = GF.primitive_elements In [36]: i = x.log(bases); i Out[36]: array([104, 240, 166, 52, 178, 118, 98, 140, 120, 202, 204, 196, 80, 136, 64, 12, 124, 142, 56, 106, 144, 84, 194, 208, 40, 20, 228, 100, 218, 96, 164, 72, 148, 68, 238, 30, 214, 18, 32, 234, 232, 162, 24, 82, 34, 158, 54, 190, 8, 10, 216, 112, 156, 50, 184, 130, 58, 16, 108, 92, 114, 152, 6, 74, 160, 206, 172, 78, 26, 138, 188, 126, 146, 182, 116, 180, 62, 38, 224, 42, 210, 186, 28, 134, 4, 102, 174, 48, 90, 86, 222, 2, 212, 150, 94, 226, 230, 128, 122, 200, 60, 236, 14, 70, 36, 192, 170, 46, 76, 168]) In [37]: np.all(bases ** i == x) Out[37]: True