The Simulation replay toolbar lets you step through a finished run on the model sketch, one moment in time at a time. As you move through the run, Vensim highlights the feedback loops on the sketch and shades each one by how strongly it is driving the model's behavior at that moment.
Use it to answer questions like "which loop is in charge here?" and "when does control shift from growth to balancing?" without leaving the sketch. You can also show each variable's behavior on the sketch, as a small graph or a filling level, so you see the numbers and the loop structure together.
The toolbar only replays runs that have already been simulated and loaded. It does not run the model.
To display the toolbar, click the 
Replay icon on the main toolbar. The Simulation replay toolbar opens as a floating toolbar. You can dock it at the top or bottom of the window. Click Replay again, or close the toolbar to hide it. Hiding it stops playback and removes the loop highlighting from the sketch.
When the toolbar opens, it reads every loaded run and selects the first one.
What a run needs for loops to appear. Time replay and behavior display work with any loaded run. Loop highlighting only works if the run's results file holds loop data. Before simulating, open Simulation Control, go to the Run Information page and, in the Structural intelligence (loop dominance) box, tick Loop impact and energy, or Eigenvalue analysis (slower) to get both kinds of analysis. See Structural Intelligence (Loop Dominance) for details.
Control |
Type |
What it does |
Runs |
Drop-down list |
Picks which loaded run to replay. Changing it clears the highlighting and resets the time range to that run. |
Refresh |
Button |
Re-reads the loaded runs and their loop data. Use it after you simulate again or load another run. Keeps your current run selected if it is still there. |
Select time |
Slider |
Sets the moment in the run you are looking at, from the run's start time to its end time. Dragging it pauses playback. |
Play |
Button |
Moves the slider forward automatically. If the slider is already at the end, it starts again from the beginning. Greyed out while playing. |
Pause |
Button |
Stops playback where it is. Greyed out unless playing. |
Continuous loop |
Toggle with drop-down arrow |
Click the button to turn looping on or off. When on, playback jumps back to the start after reaching the end; when off, it stops at the end. Click the arrow to set the speed (see below). |
Loops |
Check box |
Turns loop highlighting on or off. Ticked by default. Greyed out if the selected run has no loop data. |
Eigen |
Toggle |
Ranks loops by their eigenvalue influence: how much each loop shapes the model's dominant behavior modes. |
Loop impact |
Toggle with drop-down arrow |
Ranks loops by a loop impact measure. Click the arrow to choose Loop impact, Loop power or Loop energy (see below). Eigen and Loop impact are either/or. |
Color |
Toggle |
When on, each highlighted loop is drawn in its own color. When off (the default), all loops use the single highlight color. |
Show behavior |
Button with drop-down arrow |
Chooses how variable values are shown on the sketch: None, Mini graph, Mini graph (with time) or Levels (see below). |
The Continuous loop arrow menu sets the tool to continually repeat the animations. In addition, there is a small drop down button that can be used to control how fast the slider moves.
At each moment, Vensim ranks the loops using the chosen measure. The strongest loop on screen is drawn at full strength and the weakest is faded the most. Loops in between are shaded by how close their value is to the strongest, not just by their rank. Loops with no data yet at that moment are not drawn.
For what each measure tells you and how to interpret the shading, see Showing Loop Dominance on the Sketch.
The slider has about ten notches for every saved time step. Between saved steps, loop strength is blended smoothly, so the shading changes gradually as you drag.
•Loop impact: how strongly the loop is pushing the system right now, as a rate (per unit of time).
•Loop power: how fast the loop is transferring energy right now.
•Loop energy: the total work the loop has done since the start of the run. Useful for seeing which loop has mattered most overall, rather than at this instant.
If Loop impact is already the active measure, clicking the main part of the button also opens this menu.
Option |
What you see on the sketch |
None |
No behavior display. |
Mini graph |
A small graph of each variable over the whole run. |
Mini graph (with time) |
As Mini graph, plus a dotted vertical line marking the current replay time. |
Levels |
Each variable drawn as a tank, filled from the bottom in proportion to its value at the current replay time, with the value shown as text. Only the selected run is shown. |
Whenever any option other than None is chosen, graphs embedded in the sketch also show a dotted line at the current replay time.
1.In Simulation Control > Run Information, tick Loop impact and energy (or Eigenvalue analysis (slower)) in the Structural intelligence (loop dominance) box, then simulate.
2.Click Replay on the main toolbar.
3.Pick the run in Runs. If it isn't listed, click Refresh.
4.Make sure Loops is ticked, then choose Eigen or Loop impact (and a measure from its arrow menu).
5.Turn on Color if you want to tell loops apart.
6.Choose a Show behavior option, for example Mini graph (with time), to see values alongside the loops.
7.Click Play to watch the run, or drag Select time to jump to a moment. Use the Continuous loop arrow to slow playback down around interesting periods.
8.Click Replay again when you're done. The sketch goes back to normal.
Problem |
Likely cause and fix |
Everything on the toolbar is greyed out except Refresh |
No runs are loaded. Simulate or load a run, then click Refresh. |
Loops is greyed out |
The selected run has no loop data. Re-run with Loop impact and energy (or Eigenvalue analysis (slower)) ticked in Simulation Control, then click Refresh. |
Eigen, Loop impact and Color are greyed out |
Loops is unticked or unavailable. Tick it. |
A new run doesn't appear in the list |
The list is only read when the toolbar opens or when you click Refresh. Click Refresh. |
Loops are drawn only between stocks |
The run was saved by an older version that didn't store the loop structure. Re-run the model to get the full loop paths. |
Some loops are missing early in the run |
Those loops have no data until the first linearization point. They appear once data exists. |
Nothing happens in the text view |
Replay highlighting only works on the sketch. Switch back to the sketch view. |
