5.1.3.3. Example: Order of evaluation¶

Description: This example shows the behaviour when a reset value involves a variable.

Note that:

all elements are in the same component;
resets are shown attached to their variable attribute;
the order values of resets are not shown; and
all variables have dimensionless units.

component:
  ├─ math: ode(B, t) = 1
  │
  ├─ variable: A initially 1
  │   └─ reset: rule 1
  │       ├─ when B == 3
  │       └─ then A = B
  │
  └─ variable: B initially 1
      └─ reset: rule 2
          ├─ when B == 3
          └─ then B = 1

<variable name="t" units="dimensionless" />
<variable name="A" units="dimensionless" initial_value="1" />
<variable name="B" units="dimensionless" initial_value="1" />

<math>
    <apply><eq/>
        <diff>
            <ci>B</ci>
            <bvar>t</bvar>
        </diff>
        <cn cellml:units="dimensionless">1</cn>
    </apply>
</math>

<!-- Reset rule 1: -->
<reset variable="A" test_variable="B">
    <test_value>
        <cn units="cellml:dimensionless">3</cn>
    </test_value>
    <reset_value>
        <ci>B</ci>
    </reset_value>
</reset>

<!-- Reset rule 2: -->
<reset variable="A" test_variable="B">
    <test_value>
        <cn units="cellml:dimensionless">3</cn>
    </test_value>
    <reset_value>
        <ci>B</ci>
    </reset_value>
</reset>

At t = 2 the following situation occurs:

t	0	1	2
A	1	1	1
B	1	2	3

At this point \((x, t, p)\), the test conditions for both resets are true, so both are active. New values are first calculated, and then applied to yield a new point \((x^\prime, t, p)\):

t	0	1	2
A	1	1	1 → 3
B	1	2	3 → 1

Note that both tests are performed using \((x, t, p)\), so the order of these tests doesn’t change the outcome. Secondly, because the changes are orthogonal (each reset affects a different node in the directed acyclic graph), we can apply them in any order and reach the same point \((x^\prime, t, p)\).

Because \((x^\prime,t, p) \neq (x, t, p)\) a second round of reset evaluation is started, but no active resets are found, the reset evaluation is halted and model dynamics continue.

t	0	1	2	2 + dt	3
A	1	1	1 → 3	3	3
B	1	2	3 → 1	1 + dt	2