Fluence for the source collection was not calculated properly in the case of a collection consisting of N transformations, i, of a single base source. EGS_SourceCollection::getFluence() sums the results of getFluence() for the i individual sources. If they are transformations of a single base source, then for each source i, getFluence returns the total fluence (of the base source), F_tot. Thus, EGS_SourceCollection::getFluence() erroneously returns N*F_tot.

The solution is to "detect" a group of sources sharing a common base source by looking for increases in the fluence of source i != j, where j is the source in the collection from which a given particle is being sampled. Before summing individual source fluences, EGS_SourceCollection::getFluence() then multiplies the result of getFluence() for source i by p[i]/p_tot, where p[i] is the user input probability for source i and p_tot is the sum of all probabilities of the N sources sharing the same base source. We are thus able to obtain an estimate of the fluence from each source i.

A further issue occurs when the results of parallel runs are combined. During a parallel run, we store the fluence for each source, i, in the source collection in the .egsdat file from each job. On recombining, results are first added up for each source. If these share a common base source, then these separate additions are actually cumulative with respect to the base source, with the result being that each source, i, will have (erroneous) fluence NF_tot. Then, to obtain the fluence of the source collection, we sum over the N sources, resulting in an additional multiplicative factor of N, so the total fluence is NN*F_tot. In this fix, we now detect when results are being combined and, prior to summing fluence from individual sources, divide by an additional factor N. Note that in order to determine N, we make use of new information written to the .egsdat file for each source i listing the other sources j != i sharing a common base source.

Fixes issue #1065