5.1.3.5. Example: Using variables as reset values

Description: A simple example demonstrating the behaviour where one variable is reset to the value of another.

Note that:

• all elements are in the same component;

• 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 == 4
  │       └─ then A = A + 1
  │
  └─ variable: B initially 3
      └─ reset: rule 2
          ├─ when A == 2
          └─ then B = A + B

See CellML syntax

<variable name="t" units="dimensionless" />
<variable name="A" units="dimensionless" initial_value="1" />
<variable name="B" units="dimensionless" initial_value="3" />

<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">4</cn>
    </test_value>
    <!-- Variable A is given a value of A+1 when B equals 4. -->
    <reset_value>
        <apply><plus/>
            <ci>A</ci>
            <cn cellml:units="dimensionless">1</cn>
        </apply>
    </reset_value>
</reset>

<!-- Reset rule 2: -->
<reset variable="B" test_variable="A">
    <test_value>
        <cn units="cellml:dimensionless">2</cn>
    </test_value>
    <!-- Variable B is given a value of A+B when A equals 2. -->
    <reset_value>
        <apply><plus/>
            <ci>A</ci>
            <ci>B</ci>
        </apply>
    </reset_value>
</reset>

At t = 1 the following situation occurs:

t	0	1
A	1	1
B	3	4

At this point, reset rule 1 for A is active. Its new value is calculated to be A → A + 1 = 1 + 1 = 2.

t	0	1
A	1	1 → 2
B	3	4

This is a new point, so reset evaluation enters a second cycle. In this cycle, the resets for both A and B are active. The new values are calculated to be A → A + 1 = 2 + 1 = 3, and B → A + B = 2 + 4 = 6. The new values are applied:

t	0	1
A	1	1 → 2 → 3
B	3	4 → 6

A new cycle of reset evaluation is applied, but finds no active resets, so model dynamics continue.