cotd — cotangent
y=cotd(x)
The entries of y are the cotangents of the
corresponding entries of x supposed to be given in
degree. t=cos(x)./sin(x). For entries equal to
n*180 with n integers the results
are infinite, whereas cotg(n*%pi) is large but finite
because %pi cannot be represented exactly. For entries
equal to n*90 with n integers and
odd the results are exactly 0.