Properly calculate the index into a compacted symmetric array

Dr15Jones · Dr15Jones · commit 292e51a61c1b · 2021-05-14T14:23:02.000-05:00
diff --git a/CondFormats/EcalObjects/interface/EcalPulseSymmCovariances.h b/CondFormats/EcalObjects/interface/EcalPulseSymmCovariances.h
@@ -17,7 +17,7 @@ struct EcalPulseSymmCovariance {
   int indexFor(int i, int j) const {
     int m = std::min(i, j);
     int n = std::max(i, j);
-    return n + (EcalPulseShape::TEMPLATESAMPLES - 1) * m;
+    return n + EcalPulseShape::TEMPLATESAMPLES * m - m * (m + 1) / 2;
   }
 
   float val(int i, int j) const { return covval[indexFor(i, j)]; }

Original file line number	Diff line number	Diff line change
`@@ -17,7 +17,7 @@ struct EcalPulseSymmCovariance {`
`17`	`17`	`int indexFor(int i, int j) const {`
`18`	`18`	`int m = std::min(i, j);`
`19`	`19`	`int n = std::max(i, j);`
`20`		`- return n + (EcalPulseShape::TEMPLATESAMPLES - 1) * m;`
	`20`	`+ return n + EcalPulseShape::TEMPLATESAMPLES * m - m * (m + 1) / 2;`
`21`	`21`	`}`
`22`	`22`
`23`	`23`	`float val(int i, int j) const { return covval[indexFor(i, j)]; }`