Generalized weight-aggregation functions instead of only +
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Made some simple changes to use a function `waf`, short for `weight-aggregation function`. Defaults to `+`, as the affected graph functions previously implicitly used. Affected functions include `dijkstra-traverse`, `dijkstra-span`, `bellman-ford-transform`, and `johnson`. The reason for this commit is that weights won't always be simply added - they might be multiplied, subtracted, or divided. Suppose one were to perform unit conversion, for instance, where to get from one unit to another one would multiply by a constant (or equivalently, divides by the inverse of the constant). To aggregate the conversions needed from seconds to nanoseconds using `all-pairs-shortest-paths`, one would need to not *add* 1/1000 to get to milliseconds, then another 1/1000 to get to microseconds, then another to get to nanoseconds, but rather to *multiply* them. There are certainly examples when weight-aggregation functions might be more complex than simply `*` or `+`, but I will not touch on them here.
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Made some simple changes to use a function
waf, short forweight-aggregation function. Defaults to+, as the affected graph functions previously implicitly used.Affected functions include
dijkstra-traverse,dijkstra-span,bellman-ford-transform, andjohnson.The reason for this commit is that weights won't always be simply added: they might be multiplied, subtracted, or divided. Suppose one were to perform unit conversion, for instance, where to get from one unit to another one would multiply by a constant (or equivalently, divides by the inverse of the constant). To aggregate the conversions needed from seconds to nanoseconds using
all-pairs-shortest-paths, one would need to not add 1/1000 to get to milliseconds, then another 1/1000 to get to microseconds, then another to get to nanoseconds, but rather to multiply them, resulting in a conversion factor of 1/1,000,000,000. There are certainly examples when weight-aggregation functions might be more complex than simply*or+, but I will not touch on them here.