Where does source collide?

In a flow network the source is the distinguished vertex where flow originates: the single node, paired with a sink, from which everything in a maximum-flow problem departs. Ford and Fulkerson (1956) formalised it while proving the max-flow min-cut theorem, treating the network as a directed graph with a capacity on every edge and asking how much can be pushed from source s to sink t. The referent is a labelled vertex in a combinatorial structure, and its unit is the rate of flow leaving that node, bounded by the capacities of its outgoing edges. It carries no water and holds no meaning; it is a position in a graph. The same s reappears in routing, bipartite matching, and image segmentation, always as the origin against which a cut is measured.[1]

Unit

A distinguished origin vertex and the flow rate leaving it

Recovery means

Not applicable

Measured by

Outflow value, outgoing edge capacities, and the maximum flow from source to sink

In population ecology a source is a habitat patch where local reproduction exceeds local mortality, so it produces a net surplus of individuals that emigrate to sustain poorer patches. Pulliam (1988) defined source-sink dynamics with a demographic balance sheet: in a source, births plus immigration outrun deaths plus emigration, giving a finite rate of increase above one, while a sink runs a deficit and persists only on the overflow. The referent is a place characterised by its per-capita demographic rates, not the organisms standing in it, and its unit is the net reproductive surplus a patch exports per generation. A patch can look crowded and be a sink, or look sparse and be a source; only the vital rates decide. It shares the word with a graph vertex and an archival document but names a demographic role.[2]

Unit

A habitat patch and the net reproductive surplus it exports

Recovery means

Not applicable

Measured by

Birth and death rates, immigration and emigration, and the finite rate of increase

In physics a source is whatever generates a field: the charge and current densities that produce electromagnetic fields, or the inhomogeneous term on the right side of a field equation. In Maxwell's equations as codified by Jackson (1998), charge is the source of the electric field and current the source of the magnetic field; a point source is an idealised origin from which a field radiates, and the field's Green's function is the response to a unit source. The referent is a physical density or its idealisation, and its unit is a source strength, a charge per volume or a current, that fixes the field's magnitude. It shares the word with a graph vertex and a document but names a cause inside a differential equation, the term whose absence would leave the homogeneous, source-free field.[3]

Unit

A charge or current density, or the inhomogeneous term it supplies

Recovery means

Not applicable

Measured by

Source strength, charge and current density, and the resulting field magnitude

In journalism a source is a person or organisation that supplies a reporter with information: the official, witness, or insider whose account becomes the raw material of a story. Gans (1979), studying network news and newsmagazines, described the relation as a tug of war in which sources seek access and reporters seek information, each managing the other, so that who counts as a source shapes what the public learns. The referent is a human informant embedded in a relationship of exchange and trust, and its unit is an attributed or anonymous account offered to a journalist. Its worth turns on access, credibility, and motive, not on capacity or vital rates. A whistleblower, a press officer, and an eyewitness are all sources, and protecting or naming one is itself a contested act.[4]

Unit

A human informant and the account they supply a reporter

Recovery means

Not applicable

Measured by

Access, credibility, motive, and whether the account is attributed or anonymous