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Efficiency: use multiplication over std::pow for squaring (#3373) #3375

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Merged
WardBrian merged 3 commits into from
Aug 28, 2026
+6 −3
Merged

Efficiency: use multiplication over std::pow for squaring (#3373) #3375

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0c82cc9
Efficiency: use multiplication over std::pow for squaring (#3373)
Purna-Chandra-4706 Aug 25, 2026
05e4a1a
Efficiency: update squared_distance to use multiplication instead of pow
Purna-Chandra-4706 Aug 25, 2026
c98e30e
Refactoring squared_distance to use multiplication instead of pow.
Purna-Chandra-4706 Aug 26, 2026
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3 changes: 2 additions & 1 deletion stan/math/prim/fun/square.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,8 @@ namespace math {
*/
template <typename T, require_arithmetic_t<T>* = nullptr>
inline double square(const T x) {
return std::pow(x, 2);
double x_dbl = x;
return x_dbl * x_dbl;
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}

/**
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6 changes: 4 additions & 2 deletions stan/math/rev/fun/squared_distance.hpp
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Expand Up @@ -21,7 +21,8 @@ namespace math {
inline var squared_distance(const var& a, const var& b) {
check_finite("squared_distance", "a", a);
check_finite("squared_distance", "b", b);
return make_callback_vari(std::pow(a.val() - b.val(), 2),
double difference = a.val() - b.val();
return make_callback_vari(difference * difference,
[a, b](const auto& vi) mutable {
const double diff = 2.0 * (a.val() - b.val());
a.adj() += vi.adj_ * diff;
Expand All @@ -35,7 +36,8 @@ inline var squared_distance(const var& a, const var& b) {
inline var squared_distance(const var& a, double b) {
check_finite("squared_distance", "a", a);
check_finite("squared_distance", "b", b);
return make_callback_vari(std::pow(a.val() - b, 2),
double difference = a.val() - b;
return make_callback_vari(difference * difference,
[a, b](const auto& vi) mutable {
a.adj() += vi.adj_ * 2.0 * (a.val() - b);
});
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