2.2. Closing a Model
31
When your model becomes increasingly complicated, try to keep your
STELLA diagram as organized as possible , so it clearly shows the interrelations among the model parts. A strong point of STELLA is its ability to maintain transparency in the interrelationships among the many components of
a complicated model. Use the hand symbol to move model parts around
the diagram ; use the paintbrush to change the color of icons.
With each additional feature , the diagram of the model increases in size.
In larger models that have highly interdependent components, we need to
make a large number of connections. With an increasing number of connections, or information arrows , the readability of the model can be seriously reduced. Use "Ghosts" of icons to avoid crossing arrows and by doing
so increase the transparency of the model structure . You can create a ghost,
for example, of a translation variable by first clicking on the ghost icon
shown on the right in Figure 2.14.
Once you clicked on the ghost icon, move it to and click on the variable
that you want to duplicate. The ghost icon then changes its appearance into
that of the icon on which you clicked. You can now place this duplicate of
the original anywhere in the diagram and connect it with information arrows to the relevant parts of the model. The ghost you created is the same
icon as its original, but printed slightly lighter in color than the original. Notice that changes to a particular model component must be made to the
original, not the ghost-the ghost will assume that change after it has been
made to the original.
The dynamite (shown in Figure 2.14 to the left of the ghost) will blast off
any unnecessary parts of the model. Be careful when you blast away information arrows . Move the dynamite to the place where the information
arrow is attached and click on the spot. If you click, for example, on the
translation variable itself, it will disappear, together with the information
arrow , and you may have to recreate it.
The paint brush can be used to color-code individual parts of the model.
You may want to give the same color to all those elements for which you
still need better data , or all those elements whose specification is derived
on the basis of field or lab experiments. Develop your own color-coding
and be able to quickly discern from the model where potential crucial assumptions are made , where better data is needed or where refinements are
in order.
By annotating the model , you can remind yourself and inform others of
the assumptions underlying your model and its submodels. This is important in any model , but especially in larger and more complicated models.
F,GURE 2.14
31
When your model becomes increasingly complicated, try to keep your
STELLA diagram as organized as possible , so it clearly shows the interrelations among the model parts. A strong point of STELLA is its ability to maintain transparency in the interrelationships among the many components of
a complicated model. Use the hand symbol to move model parts around
the diagram ; use the paintbrush to change the color of icons.
With each additional feature , the diagram of the model increases in size.
In larger models that have highly interdependent components, we need to
make a large number of connections. With an increasing number of connections, or information arrows , the readability of the model can be seriously reduced. Use "Ghosts" of icons to avoid crossing arrows and by doing
so increase the transparency of the model structure . You can create a ghost,
for example, of a translation variable by first clicking on the ghost icon
shown on the right in Figure 2.14.
Once you clicked on the ghost icon, move it to and click on the variable
that you want to duplicate. The ghost icon then changes its appearance into
that of the icon on which you clicked. You can now place this duplicate of
the original anywhere in the diagram and connect it with information arrows to the relevant parts of the model. The ghost you created is the same
icon as its original, but printed slightly lighter in color than the original. Notice that changes to a particular model component must be made to the
original, not the ghost-the ghost will assume that change after it has been
made to the original.
The dynamite (shown in Figure 2.14 to the left of the ghost) will blast off
any unnecessary parts of the model. Be careful when you blast away information arrows . Move the dynamite to the place where the information
arrow is attached and click on the spot. If you click, for example, on the
translation variable itself, it will disappear, together with the information
arrow , and you may have to recreate it.
The paint brush can be used to color-code individual parts of the model.
You may want to give the same color to all those elements for which you
still need better data , or all those elements whose specification is derived
on the basis of field or lab experiments. Develop your own color-coding
and be able to quickly discern from the model where potential crucial assumptions are made , where better data is needed or where refinements are
in order.
By annotating the model , you can remind yourself and inform others of
the assumptions underlying your model and its submodels. This is important in any model , but especially in larger and more complicated models.
F,GURE 2.14