#131 - Matrix power via square decomposition, v2#134
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| function IntervalMatrixPower(M::IntervalMatrix{T}, k::Int) where {T} | ||
| function IntervalMatrixPower(M::IntervalMatrix{T}, k::Int; | ||
| algorithm::String="power") where {T} |
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Should algorithm be a field of the type?
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I was also thinking about that. It is more general to let you choose at every step, but we could at least have a fallback algorithm defined in the type maybe?
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At first sight it looks better to me if the algorithm is in the type, since it is a property of how to get to M^k, and also how to get higher powers. (Of course i'm assuming that there is no mixed algorithm, but the "mixed" algorithm can be an algorithm by itself).
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Anyway, we can revisit this later.
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(Of course i'm assuming that there is no mixed algorithm, but the "mixed" algorithm can be an algorithm by itself).
Yes and no. If the mixed algorithm follows a strict pattern, it can be added as another algorithm. But adding a new algorithm for any pattern is not sustainable. Furthermore, you can imagine patterns that depend on user knowledge (like "next I need more precision") that you cannot express in a static algorithm. So I conclude that a String as a field is not sufficient. If we make the algorithm a field, it should be its own struct <:IntervalMatrixPowerAlgorithm that you can influence from outside.
| b = k - a^2 | ||
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| # recursively compute M^a and M^b | ||
| Mᵏ = square(get(IntervalMatrixPower(pow.M, a; algorithm=algorithm))) |
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Is line 178 the same as get(IntervalMatrixPower(pow.M, a*a) ? (Also, this is the functionality that i was asking in this comment. I'll create an issue).
EDIT: This is now #138.
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My question still is why not use get(IntervalMatrixPower(pow.M, a*a; algorithm=algorithm))) here.
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why not use
get(IntervalMatrixPower(pow.M, a*a; algorithm=algorithm)))here.
Because it is not equivalent. We do not use square for arbitrary square numbers but only for powers of 2.
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Oh, damn, your version was the correct one:
A^(a²) = A^(a*a) = (A^a)^a != (A^a)² for a != 2
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Closes #131.
Currently the algorithm for the recursive call cannot be changed.