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Update Math.Vectors.interpolate #4641

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5575c6e
Update Math.Vectors.interpolate
DagBruck May 12, 2025
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Merge branch 'master' into DagBruck-math-1
DagBruck May 19, 2025
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38 changes: 23 additions & 15 deletions Modelica/Math/package.mo
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Original file line number Diff line number Diff line change
Expand Up @@ -497,10 +497,10 @@ can be provided as third argument of the function. Default is \"eps = 0\".
function interpolate "Interpolate linearly in a vector"
extends Modelica.Icons.Function;
input Real x[:]
"Abscissa table vector (strict monotonically increasing values required)";
"Abscissa table vector (monotonically increasing values required)";
input Real y[size(x, 1)] "Ordinate table vector";
input Real xi "Desired abscissa value";
input Integer iLast=1 "Index used in last search";
input Integer iLast=0 "Index used in last search (optional)";
output Real yi "Ordinate value corresponding to xi";
output Integer iNew=1 "xi is in the interval x[iNew] <= xi < x[iNew+1]";
protected
Expand All @@ -516,18 +516,23 @@ can be provided as third argument of the function. Default is \"eps = 0\".
yi := y[1];
else
// Search interval
i := min(max(iLast, 1), nx - 1);
if xi >= x[i] then
// search forward
while i < nx and xi >= x[i] loop
i := i + 1;
end while;
i := i - 1;
if (nx == 2) then
i := 1;
else
// search backward
while i > 1 and xi < x[i] loop
i := if iLast >= 1 then iLast else integer((xi-x[1]) / (x[nx]-x[1]) * nx);
i := min(max(i, 1), nx - 1);
if xi >= x[i] then
// search forward
while i < nx and xi >= x[i] loop
i := i + 1;
end while;
i := i - 1;
end while;
else
// search backward
while i > 1 and xi < x[i] loop
i := i - 1;
end while;
end if;
end if;

// Get interpolation data
Expand All @@ -536,9 +541,12 @@ can be provided as third argument of the function. Default is \"eps = 0\".
y1 := y[i];
y2 := y[i + 1];

assert(x2 > x1, "Abscissa table vector values must be increasing");
// Interpolate
yi := y1 + (y2 - y1)*(xi - x1)/(x2 - x1);
if x2 > x1 then
// Interpolate
yi := y1 + (y2 - y1)*(xi - x1)/(x2 - x1);
else
yi := y2;
end if;
iNew := i;
end if;

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