Improve loop order in matmul

simonlindholm · simonlindholm · commit c1bfa264949e · 2025-11-14T13:39:32.000+01:00
Fixes #306.
diff --git a/content/data-structures/Matrix.h b/content/data-structures/Matrix.h
@@ -18,7 +18,7 @@ template<class T, int N> struct Matrix {
 	M operator*(const M& m) const {
 		M a;
 		rep(i,0,N) rep(j,0,N)
-			rep(k,0,N) a.d[i][j] += d[i][k]*m.d[k][j];
+			rep(k,0,N) a.d[i][k] += d[i][j] * m.d[j][k];
 		return a;
 	}
 	array<T, N> operator*(const array<T, N>& vec) const {

Original file line number	Diff line number	Diff line change
`@@ -18,7 +18,7 @@ template<class T, int N> struct Matrix {`
`18`	`18`	`M operator*(const M& m) const {`
`19`	`19`	`M a;`
`20`	`20`	`rep(i,0,N) rep(j,0,N)`
`21`		`- rep(k,0,N) a.d[i][j] += d[i][k]*m.d[k][j];`
	`21`	`+ rep(k,0,N) a.d[i][k] += d[i][j] * m.d[j][k];`
`22`	`22`	`return a;`
`23`	`23`	`}`
`24`	`24`	`array<T, N> operator*(const array<T, N>& vec) const {`