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Issue1840 interpolate not smooth #1841

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Feb 28, 2024
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Issue1840 interpolate not smooth #1841

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b2076fc
deleted unneeded code
hcasperfu Feb 26, 2024
9177da9
added smoothOrder annotation
hcasperfu Feb 26, 2024
49172ae
updated results
hcasperfu Feb 26, 2024
760e195
updated change log
hcasperfu Feb 26, 2024
aa019c0
Updated comment
mwetter Feb 27, 2024
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2 changes: 1 addition & 1 deletion IBPSA/Airflow/Multizone/BaseClasses/Examples/Interpolate.mo
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
within IBPSA.Airflow.Multizone.BaseClasses.Examples;
model Interpolate "Test model for the function flowElementData"
model Interpolate "Test model for the interpolation function"
extends Modelica.Icons.Example;

parameter Real table[:,:]=[-50,-0.08709; -25,-0.06158; -10,-0.03895; -5,-0.02754;
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35 changes: 17 additions & 18 deletions IBPSA/Airflow/Multizone/BaseClasses/interpolate.mo
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Expand Up @@ -21,29 +21,22 @@ algorithm
end if;
end for;

// Extrapolate or interpolate the data
if i == 1 then
z:=yd[1]+(u-xd[1])*(yd[2]-yd[1])/(xd[2]-xd[1]); //Interpolate linearly between first and second point
elseif i == (size(xd, 1) - 1) then
z:=yd[end-1]+(u-xd[end-1])*(yd[end]-yd[end-1])/(xd[end]-xd[end-1]); //Interpolate linearly between last and second-to-last point.
z :=IBPSA.Utilities.Math.Functions.cubicHermiteLinearExtrapolation(
x=u,
x1=xd[i],
x2=xd[i + 1],
y1=yd[i],
y2=yd[i + 1],
y1d=d[i],
y2d=d[i + 1]);

else
z :=IBPSA.Utilities.Math.Functions.cubicHermiteLinearExtrapolation(
x=u,
x1=xd[i],
x2=xd[i + 1],
y1=yd[i],
y2=yd[i + 1],
y1d=d[i],
y2d=d[i + 1]);
end if;

annotation (
annotation (smoothOrder = 1,
Documentation(info="<html>
<p>
This function returns the value on a cubic hermite spline through the given support points
and provided spline derivatives at these points with monotonically increasing values.
The last 2 points in the table are linearly interpolated.
Outside the provided support points, the function returns a linear extrapolation with
the same slope as the cubic spline has at the respective support point.
</p>
<p>
A similar model is also used in the CONTAM software (Dols and Walton, 2015).
Expand All @@ -67,6 +60,12 @@ National Institute of Standards and Technology, NIST TN 1887, Sep. 2015. doi:
</html>", revisions="<html>
<ul>
<li>
February 26, 2024, by Hongxiang Fu:<br/>
Correct implementation to make it smooth.<br/>
This is for
<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/1840\">IBPSA, #1840</a>.
</li>
<li>
February 2, 2022, by Michael Wetter:<br/>
Revised implementation.<br/>
This is for
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