std::atan

From Cppreference

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Defined in header <cmath>
float       atan( float arg );
double      atan( double arg );
long double atan( long double arg );

Computes arc tangent of arg

[edit] Parameters

arg

-

floating point value

[edit] Return value

arc tangent of arg in radians in the range of [-π/2; π/2] radians.

[edit] See also

atan2	arc tangent, using signs to determine quadrants (function)
asin	computes arc sine (arcsin(x)) (function)
acos	computes arc cosine (arccos(x)) (function)
tan	computes tangent (tan(x)) (function)