`make-preferential-depth-first-world`procedure`make-preferential-depth-first-world``n-nodes`procedureCreate a random-graph using depth-first search that nevertheless shows preference for connected nodes (á la Barabási-Albert).

The graph has no cycles.

`n-nodes`- The number of nodes in the graph (default: (default-n-nodes))

(define make-preferential-depth-first-world (case-lambda (() (make-preferential-depth-first-world (default-n-nodes))) ((n-nodes) (let* ((world (make-seed-world)) (start (random-start world))) (let iter ((node start) (n-nodes (max 0 (- n-nodes (count-nodes world)))) (n-degrees (count-degrees world))) (if (zero? n-nodes) world (let ((location (hash-table-ref/default world node (make-dirty-location)))) (let ((n-neighbors (n-neighbors location))) (if (and (< n-neighbors 4) (< (bsd-random-real) (/ n-neighbors n-degrees))) (let* ((new-directions (vector-fold (lambda (direction directions neighbor) (if (no-passage? neighbor) (cons direction directions) directions)) '() (location-neighbors location))) (new-direction (list-ref new-directions (bsd-random (length new-directions))))) (let ((new-node (make-node))) (connect! world node new-node new-direction) (iter new-node (- n-nodes 1) (+ n-degrees 2)))) (let* ((neighbors (vector-fold (lambda (direction neighbors neighbor) (if (passage? neighbor) (cons neighbor neighbors) neighbors)) '() (location-neighbors location))) (neighbor (list-ref neighbors (bsd-random (length neighbors))))) (iter neighbor n-nodes n-degrees)))))))))))