atan(x [, degrees:T or radians:T or cycles:T]), x REAL or a structure with REAL components; value in radians (default), cycles, or degrees as specified by option 'angles' or the optional keyword atan(x,y [, degrees:T or radians:T or cycles:T]), y REAL or a structure with real components the same size and shape as x |

atan(x) transforms the elements of REAL vector, matrix, or array x to inverse tangents (arctangents). When x is a structure with components x1,...,xm, atan(x) is a structure with components atan(x1),...,atan(xm). When any element of x is MISSING, the corresponding element of atan(x) is MISSING. atan(x,y) computes theta = arctan(x/y), with the result in the appropriate quadrant, where x and y must be REAL vectors, matrices, or arrays with the same dimensions. Specifically, theta is chosen so that sin(theta) has the same sign as x, cos(theta) has the same sign as y and tan(theta) = x/y. atan(x,y) is also defined when x and y are both structures with the same number of components, say x is structure(x1,...,xm) and y is structure(y1,..., ym) . The result is what would be produced by structure(atan(x1,y1),...,atan(xm,ym)). The units of the result of atan(x) and atan(x,y) are radians, degrees or cycles as determined by the value of option 'angles'. The default is radians. See subtopic 'options:"angles"'. atan(x, radians:T), atan(x, degrees:T), atan(x, cycles:T), atan(x, y, radians:T), atan(x, y, degrees:T) and atan(x, y, cycles:T) return values in the specified units, overriding option 'angles'. See topic 'transformations' for more information about atan(), including its use with a CHARACTER argument. See also topics 'structures', 'labels'.

Gary Oehlert 2003-01-15