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atan2(y, x) computes the arctangent of the complex number .
This function can be used to transform from Cartesian into polar coordinates and allows to determine the angle in the correct quadrant. To convert from Cartesian Coordinates to polar coordinates (削除) (追記) (追記ここまで):(r,\\theta) (削除ここまで)
\\begin{aligned}
r &= \\sqrt{x^2 + y^2} \\\\
\\theta &= \\tan^{-1}(y / x)
\\end{aligned}
(削除ここまで)FORTRAN 77 and later
result = atan2(y, x)y - The type shall be real.x - The type and kind type parameter shall be the same as y. If y is zero, then x must be nonzero.The return value has the same type and kind type parameter as y. It is the principal value of the complex number . If x is nonzero, then it lies in the range (削除) (追記) (追記ここまで). The sign is positive if -\\pi \\leq \\atan (x) \\leq \\pi (削除ここまで)y is positive. If y is zero, then the return value is zero if x is strictly positive, (削除) (追記) (追記ここまで) if \\pi (削除ここまで)x is negative and y is positive zero (or the processor does not handle signed zeros), and (削除) (追記) (追記ここまで) if -\\pi (削除ここまで)x is negative and y is negative zero. Finally, if x is zero, then the magnitude of the result is (削除) (追記) (追記ここまで).\\pi/2 (削除ここまで)
program test_atan2
real(4) :: x = 1.e0_4, y = 0.5e0_4
x = atan2(y,x)
end program test_atan2Note: In Return value, NNemec changed the first (削除) (追記) (追記ここまで) to \\leq (削除ここまで)(削除) (追記) (追記ここまで). Joe Krahn reverted the edit, following the Fortran 2008 specs.\\lt (削除ここまで)