ReactionPath diagram ignores 'scale' option when using 'OneWayFlow' option

[speth]

If scale is set to 1.0, then the fluxes in the graphviz diagram should match the actual molar fluxes (e.g. those shown by ReactionPathDiagram.get_data(). This happens when flow_type is set to NetFlow, but not when it is set to OneWayFlow.

import os
import sys

import cantera as ct

gas = ct.Solution('gri30.xml')
gas.TPX = 1400, ct.one_atm, 'N2:1, NO:1e-3, NO2:1e-3, OH:1e-6, HO2:1e-5, HNO:1e-4, H:1e-7'

diagram = ct.ReactionPathDiagram(gas, 'N')

diagram.scale = 1.0
diagram.threshold = 1e-10
diagram.flow_type = 'OneWayFlow'

dot_file = 'rxnpath.dot'
img_file = 'rxnpath.png'
img_path = os.path.join(os.getcwd(), img_file)
print(diagram.get_data())

diagram.write_dot(dot_file)
print("Wrote graphviz input file to '{0}'.".format(os.path.join(os.getcwd(), dot_file)))
os.system('dot {0} -Tpng -o{1} -Gdpi=200'.format(dot_file, img_file))
print("Wrote graphviz output file to '{0}'.".format(img_path))

Produces the diagram:

which shows (for starters):

• scale should be 1.0, not 0.0042
• the flux from HNO to NO should be 0.0042, not 1.0

Originally reported in the Users' Group: https://groups.google.com/forum/#!topic/cantera-users/Gy1QjyuMzA8