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Correct unit delay #4651

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Correct unit delay #4651

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ce126f8
Updated
HansOlsson May 23, 2025
9a741ca
AddTestShowingIt
HansOlsson May 23, 2025
776052e
TestFunctionality
HansOlsson May 23, 2025
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10 changes: 8 additions & 2 deletions Modelica/Blocks/Discrete.mo
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Original file line number Diff line number Diff line change
Expand Up @@ -112,13 +112,17 @@ values of the last two sampled input signals.
parameter Real y_start=0 "Initial value of output signal";
extends Interfaces.DiscreteSISO;

protected
Real u_internal;
equation
when sampleTrigger then
y = pre(u);
y = pre(u_internal);
u_internal = u;
end when;

initial equation
y = y_start;
y = y_start;
u_internal = y_start;
annotation (
Documentation(info="<html>
<p>
Expand All @@ -135,6 +139,8 @@ previous sample instant. Before the second sample instant,
the output y is identical to parameter yStart.
</p>

</html>", revisions="<html>
<p>May 23, 2025 - updated to work without requiring a sampled input, but work the same if the input was sampled.</p>
</html>"), Icon(
coordinateSystem(preserveAspectRatio=true,
extent={{-100.0,-100.0},{100.0,100.0}}),
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5 changes: 5 additions & 0 deletions ModelicaTest/Blocks.mo
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Expand Up @@ -1843,6 +1843,8 @@ This shows the improvements in the numerics when balance=true is set.
annotation (Placement(transformation(extent={{0,40},{20,60}})));
Modelica.Blocks.Discrete.TriggeredMax triggeredMax
annotation (Placement(transformation(extent={{60,70},{80,90}})));
Modelica.Blocks.Discrete.UnitDelay unitDelay1(samplePeriod=samplePeriod)
annotation (Placement(transformation(extent={{0,0},{20,20}})));
equation
connect(sine.y, sampler.u)
annotation (Line(points={{-59,80},{-42,80}}, color={0,0,127}));
Expand All @@ -1864,6 +1866,9 @@ This shows the improvements in the numerics when balance=true is set.
{-52,80},{-52,96},{54,96},{54,80},{58,80}}, color={0,0,127}));
connect(booleanPulse.y, triggeredMax.trigger)
annotation (Line(points={{21,50},{70,50},{70,68.2}}, color={255,0,255}));
connect(sampler.y, unitDelay1.u) annotation (Line(points={{-19,80},{-12,80},
{-12,10},{-2,10}}, color={0,0,127}));
assert(abs(unitDelay.y-unitDelay1.y)<1e-3, "Should be the same");
annotation (experiment(StopTime=1.1));
end Discrete;

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